Physics Assertion and Reason Questions for NEET UG, Quizzes of Physics

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ASSERTION AND REASON

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1. Assertion (A): A displacement can be added with a distance. Reason (R): Adding a scalar to a vector of the same dimensions is a meaningful algebraic operation. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 2. Assertion (A): Mass, length and time may be taken as fundamental quantities. Reason (R): Mass, length and time are independent of one another. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 3. Assertion (A): If ris the position vector

then dimensions of

2 2

d r dt

is [M LT^0 1 −^2 ].

Reason (R): Dimensions of

2 2

d r (^) dt dt

      is

[M L T^0 1 −^1 ] where r→position vector,

t→ time. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

4. Assertion (A): The error in measurement of radius of the sphere is 0.3%. The permissible error in its surface area is 1.2%. Reason (R): Area of sphere, A 4 r^2 A^4 r. A r

=   ^ = 

(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

5. Assertion (A): Mean absolute error of a measurement is always positive. Reason (R): Mean absolute error is defined as the magnitude of difference between true value and measured value. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 6. Assertion (A): In mechanics the method of dimensions can't be applied to derive formula of a physical quantity which depends on more than three physical quantities. Reason (R): We can derive relation of a physical quantity with other physical quantities out of which two have same dimensions. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 7. Assertion (A): Only like quantities can be added or subtracted from each other. Reason (R): Velocity can be subtracted from the velocity gradient. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 8. Assertion (A): If a physical quantity has a unit it must have dimension. Reason (R): There may exist a physical quantity which has dimension but no unit. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

1. Units and Measurements

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9. Assertion (A): Pressure at height (z) and

temp (q) is given by

z P ek

 =^   

, K is Boltzmann constant then b may represent volume. Reason (R): Acceleration, force and work (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

10. Assertion (A): When we change the unit of measurement of a quantity, its numerical value changes. Reason (R): Smaller the unit of measurement smaller is its numerical value. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 11. Assertion (A): If the measuring instruments used are perfect, then measurements made will be perfect. Reason (R): Measurements depend upon only on the instruments. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 12. Assertion (A): When an algebraic equation has been derived, it is advisable to check it for dimensional consistency. Reason (R): This guarantees that the equation is correct. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 13. Assertion (A): eV and joule are the S.I. units of energy used in modern physics and mechanics respectively. Reason (R): Different types of energies require different units in S.I. units. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 14. Assertion (A): Pressure and energy density have same units in SI. Reason (R): Dimensions of energy density and pressure are same. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 15. Assertion (A): The dimensions of base (fundamental) quantity in other base quantities is always zero. Reason (R): All derived quantities may be represented dimensionally in terms of fundamental quantities. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 16. Assertion (A): A unitless quantity never has a non-zero dimension. Reason (R): A dimensionless quantity never has a unit. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 17. Assertion (A): Light year and wavelength have same dimensions. Reason (R): Light year represent time while wavelength represent distance. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 18. Assertion (A): Angle and strain are dimensionless. Reason (R): Angle and strain have no unit. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

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7. Assertion (A): A student performed an experiment by moving a certain block in a straight line. The velocity position graph cannot be as shown.

Reason (R): When a particle is at its maximum position in rectilinear motion its velocity must be zero. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

8. Assertion (A): When a particle is observed from two different inertial reference frames the general shape of the trajectory of particle is same. Reason (R): The position vector of a particle and its velocity are frame independent quantities. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 10. Assertion (A): The speedometer of an automobile measures the average speed of the automobile. Reason (R): Average velocity is equal to total distance divided by total time taken. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 11. Assertion (A): Two bodies of masses M and m (M > m) are allowed to fall from the same height if the air resistance force for each be the same then both the bodies will reach the earth simultaneously. Reason (R): For same air resistance, acceleration of both the bodies will be same. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 12. Assertion (A): The average speed of an object may be equal to arithmetic mean of individual speeds. Reason (R): The average speed is equal to total distance travelled per total time taken. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 13. Assertion (A): Displacement of a body is vector sum of the area under velocity-time graph. Reason (R): Displacement is a vector quantity. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

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14. Figure shows sequence of large number

of photographs of on object moving vertically under gravity. A motion picture of this photograph is run backward.

Assertion (A): A time reversal operation changes every v to −v. Reason (R): In time reversal sequence the gravitational acceleration will appear to be upward. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

15. Assertion (A): If initial velocity is negative

but acceleration is positive then displacement of a particle can never be positive.

Reason (R): If initial velocity is negative and acceleration is positive then motion must be retarded throughout. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

16. Assertion (A): v t

and v t

are same if

particle is moving in one dimension. Reason (R): In one dimensional motion there is no component of acceleration perpendicular to velocity. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

17. Assertion (A): If velocity of a particle moving in a straight line is zero at a point, its acceleration will be zero at that point.

Reason (R): Wherevera v dv dx

= holds,

v = 0  a = 0. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

18. Assertion (A): For a moving particle on a straight line magnitude of average velocity between any two points will be less than magnitude of instantaneous velocity at every point between them. Reason (R): In x-t graph slope of chord joining two points gives average velocity between them. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

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25. Assertion (A): In one dimensional motion, area under velocity-time graph gives change in position i.e., displacement. Reason (R): In one dimensional motion, area under acceleration-time graph gives final velocity. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 26. Assertion (A): A body dropped from a height of 10 m from the ground will have the velocity 5 m/s at the height of 5 m. Reason (R): At the height of 5 m from the ground, the acceleration due to gravity is 5 m/s^2. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 27. Assertion (A): A particle moves in a straight line with constant acceleration. The average velocity of this particle can not be zero in any time interval. Reason (R): For a particle moving in straight line, the average velocity in a time

interval is alwaysu^ v 2

• , where u and v are

initial and final velocities of the particle in given time interval. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

28. Assertion (A): At any instant, acceleration of a body can change its direction without any change in the direction of velocity. Reason (R): At any instant, direction of acceleration is same as that of direction of change in velocity vector at that instant. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 29. Assertion (A): For motion from rest with constant acceleration distance time graph is a parabola, always with increasing slope. Reason (R): Speed of the body starting from rest with constant acceleration always increases linearly with time. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 30. Assertion (A): If a body moves on a straight line, magnitude of its displacement and distance covered by it must be same. Reason (R): Along a straight line, a body can move only in one direction. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

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31. Assertion (A): An object moving with a

velocity of magnitude 10 m/s is subjected to a uniform acceleration 2 m/s^2 at right angle to the initial motion. Its velocity after 5s has a magnitude nearly 14 m/s.

Reason (R): The equation v = u +atcan be applied to obtain v if (^) ais constant.

(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)

(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)

(3) (A) is true but (R) is false (4) Both (A) and (R) are false

32. Assertion (A): A coin is allowed to fall in a

train moving with constant velocity. Its trajectory is a straight line as seen by observer attached to the train.

Reason (R): An observer on ground will see the path of coin as a parabola.

(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)

(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)

(3) (A) is true but (R) is false

(4) Both (A) and (R) are false

33. Assertion (A): Two particles start moving with velocities v 1 and v 2 respectively in a plane. They can meet only if component of their velocities perpendicular to line joining them are equal.

Reason (R): Relative velocity of a body w.r.t. other body is calculated along the line joining two bodies.

(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A)

(2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A)

(3) (A) is true but (R) is false

(4) Both (A) and (R) are false

34. Assertion (A): Two balls are dropped one after the other from a tall tower. The distance between them increases linearly with time (elapsed after the second ball is dropped and before the first hits ground). Reason (R): In given situation relative acceleration is zero, whereas relative velocity is non-zero. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

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11. Assertion (A): A particle is projected from ground on a horizontal plane with speed 10 ms–^1 and angle of projection 37° with horizontal. Its velocity vector will be perpendicular to initial velocity vector after^4 s 3

Reason (R): Two vectors vand u are

perpendicular thenu.v = 0

(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

12. Assertion (A): A particle moving at constant speed and constant magnitude of radial acceleration must be undergoing uniform circular motion. Reason (R): In uniform circular motion speed cannot change as there is no tangential acceleration. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 13. Assertion (A): If separation between two particles does not change then their relative velocity will be zero. Reason (R): Relative velocity is the rate of change of position of one particle with respect to another. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 14. Assertion (A): The magnitude of velocity of A with respect to B will be always less than VA. Reason (R): The velocity of A with respect to B is given by VAB = VA −V .B (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 15. Assertion (A): In projectile motion (from ground to ground projection), horizontal range is always same for angle of projection  and (90°– ). Reason (R): Horizontal range is independent of angle of projection. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 16. Assertion (A): In projectile motion, speed always decreases. Reason (R): In presence of air drag, projectile motion is a uniformly accelerated motion. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 17. Assertion (A): When speed of projection of a body is made n times, its time of flight becomes n times. Reason (R): At this speed, the range of projectile becomes n^2 times. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 18. Assertion (A): When the range of a projectile is maximum, the time of flight is the largest. Reason (R): Horizontal range is maximum when angle of projection is 90°. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

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19. Point P is on a massless thread in an ideal pulley arrangement as shown.

Assertion (A): As point P moves from right side to left side of pulley, the magnitude of it's acceleration changes. Reason (R): The tension in massless thread remains uniform in magnitude. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

20. Assertion (A): In non-uniform circular motion, velocity vector and acceleration vector are not perpendicular to each other. Reason (R): In non-uniform circular motion, particle has normal as well as tangential acceleration. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 21. Assertion (A): If a body is in state of uniform circular motion then its velocity and acceleration both are varying. Reason (R): If magnitude of velocity is v and radius of uniform circular motion is r then magnitude of acceleration is v^2 /r. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 22. Assertion (A): A particle is moving in a circle with constant tangential acceleration such that its speed v is increasing. Angle made by resultant acceleration of the particle with tangential acceleration increases with time. Reason (R): Tangential acceleration = dv dt

and centripetal acceleration = v^2 R (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

23. Assertion (A): The equation of motion can be applied only if the acceleration is along the direction of velocity and is constant. Reason (R): In circular motion, if velocity is constant then its motion is called uniform circular motion. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 24. Assertion (A): In uniform circular motion, angular acceleration is zero. Reason (R): In uniform circular motion, acceleration is constant. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 25. Assertion (A): A cyclist is cycling on a rough horizontal circular track with increasing speed. Then the net frictional force on cycle is always directed towards centre of the circular track. Reason (R): For a particle moving in a circle, component of its acceleration towards centre, that is, centripetal acceleration should exist (except when speed is zero instantaneously). (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false ꧁ঔৣ☬✞ Chulbuli Ch@h@t ✞☬ঔৣ꧂

34. Assertion (A): In uniform circular motion of a particle, sum of power delivered to it by all the forces acting on the particle is zero. Reason (R): In uniform circular motion dot product of two perpendicular vectors, force and velocity is always zero. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 35. Assertion (A): A body having uniform speed in circular path has a variable acceleration. Reason (R): Direction of acceleration is always away from the centre. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 36. Assertion (A): In turning a vehicle safely with uniform speed in circular path friction is static in nature and towards centre. Reason (R): In turning a vehicle in circular path with increasing speed friction is kinetic in nature and tangential in direction. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 37. Assertion (A): In uniform circular motion,

magnitude of acceleration is

V^2

R

and direction is always towards the centre. Reason (R): In uniform circular motion, acceleration is constant. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

38. Assertion (A): Whenever a particle moves in a circular path with uniform speed, an acceleration exists which is directed towards the centre. Reason (R): The net acceleration of a particle in circular motion is always radially inward. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 39. Assertion (A): If the speed of a body is constant, the body cannot have a path other than a circular or straight line path. Reason (R): It is not possible for a body to have a constant speed in an accelerated motion, (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 40. Assertion (A): In circular motion, centripetal and centrifugal forces act in opposite directions and balance each other. Reason (R): Centripetal force is a pseudo force. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 41. Assertion (A): In uniform circular motion of a body, its linear speed remains constant. Reason (R): In uniform circular motion total acceleration of the body has no radial component. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

42. Assertion (A): In non-uniform circular motion, linear speed of the body is variable. Reason (R): In non-uniform circular motion, acceleration of the body is towards the centre. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 43. Assertion (A): A body is moving along a circle with a variable angular speed. Work done by centripetal force will be zero. Reason (R): In non-uniform circular motion, net force on the body is not in the radial direction. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 44. Assertion (A): A body tied to an end of a string is whirled along a vertical circle by giving some velocity at the lowest position. If the velocity becomes zero before the tension in the string is zero, the body will leave the circular path at the position of its zero velocity and then fall vertically downward. Reason (R): In vertical circular motion, tension in the string at the highest position is maximum. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 45. Assertion (A): A body tied to an end of a string is whirled along a vertical circle with such a velocity at the lowest point that, at some position, tension in the string is zero but the speed at the position is non-zero. The body will leave the circular path at the position of zero tension. Reason (R): In vertical circular motion, so as to cross the highest point along the

circle, speed at the highest point, vH^ ^0.

(1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

46. Assertion (A): Cream gets separated out of milk when it is churned. It is due to gravitational force. Reason (R): In all circular motions, centripetal force is provided by gravitational force. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 47. Assertion (A): When a stone attached to the string just rotates in a vertical circle, its apparent weight is zero at the highest point. Reason (R): At the highest point, the apparent weight is equal to mg minus tension in string. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false ꧁ঔৣ☬✞ Chulbuli Ch@h@t ✞☬ঔৣ꧂

1. Assertion (A): According to Newton's third law of motion, action and reaction forces are equal in magnitude and opposite in direction. Reason (R): Net force on a body due to action-reaction pair is always equal to zero. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 2. Assertion (A): For an upward moving elevator (Lift), pseudo force on a block may be downward. Reason (R): Pseudo force is the force applied by lift on block in opposite direction of motion. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 3. Assertion (A): When a person walks on a rough surface, the net force exerted by surface on the person is in the direction of his motion. Reason (R): Friction force by road on person is against motion. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 4. A moongphaliwala sells his moongphali using a weighing machine in an elevator. Assertion (A): He gains more profit if the elevator is accelerating up. Reason (R): The apparent weight of an object increases in an elevator while accelerating upward. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 5. Assertion (A): The driver of a moving car sees a wall in front of him. To avoid collision, he should apply brakes rather than taking a turn away from the wall. Reason (R): Friction force is needed to stop the car or taking a turn on a horizontal road. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 6. Assertion (A): A bird sits on a stretched wire depressing it slightly. The increase in tension of the wire is more than the weight of the bird. Reason (R): The tension must be more than the weight as it is required to balance weight. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 7. Assertion (A): When two particles interact, net force on either particle is zero. Reason (R): Both experience action and reaction which are equal and opposite. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 8. Assertion (A): Two smooth blocks are kept on a smooth inclined plane such that one block is kept over other. When a force is applied on upper block acceleration of lower block is unaffected. Reason (R): Acceleration of a block on smooth inclined plane is g sin. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

4. Laws of Motion

꧁ঔৣ☬✞ Chulbuli Ch@h@t ✞☬ঔৣ꧂

9. Assertion (A): A man standing at rest on

ground. Force exerted by man on ground is equal to weight of man. Reason (R): Earth attracts man by force mg hence by Newton’s third law, man also attracts earth by same force. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

10. Assertion (A): If a body has no

acceleration, then there are no forces acting on it. Reason (R): If a single force acts on a body, then the body will move in the direction of force. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

11. Assertion (A): Walking on horizontal

slippery ice can be much more tiring than walking on ordinary pavement. Reason (R): Walking on ice requires small steps to prevent slipping. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

12. Assertion (A): A particle on earth found to be at rest when seen from a frame U 1 and moving with a constant velocity when seen from another frame U 2. Then both frames may be non-inertial. Reason (R): A reference frame attached to the earth must be an inertial frame. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false 13. Assertion (A): A coin dropped in a closed trolley moving down the smooth inclined plane, appears to fall normal to the floor of the trolley to a man fixed with the trolley.

Reason (R): The acceleration of coin relative to trolley (i.e. man) is g cos downward and perpendicular to inclined plane. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false

14. Assertion (A): The contact force is the net force applied by the surface on the body kept on it. Reason (R): When a body is at rest on a horizontal surface then the contact force on the body by the surface must be equal to the weight of body. (1) Both (A) & (R) are true and the (R) is the correct explanation of the (A) (2) Both (A) & (R) are true but the (R) is not the correct explanation of the (A) (3) (A) is true but (R) is false (4) Both (A) and (R) are false