Q# no1: a) in an elastic collision between two particles, does the kinetic energy of each particle
change as a result of the collision?
Answer: In a one-dimensional collision between two identical particles with the same initial
speed, the kinetic energy of the particles will not change.
b) Three balls are thrown into the air simultaneously. What is the acceleration of their center of
mass while they are in motion?
Answer: The acceleration of their center mass wills 9.8 m/s².
c) The Moon revolves around the Earth. Model its orbit as circular. Is the Moon's linear
momentum conserved? Is its kinetic energy conserved?
Answer: No an external force of gravity acts on the moon. Yes, because its speed is constant
Q# no2: a) Does large forces always produce a larger impulse on an object than a smaller force
does?
Answer: It is possible for an object to obtain a larger impulse from a smaller force than it does
from a larger force. Impulse is the product of both net force and time. A large impulse could be
obtained from a small force if the small force acts for a long period of time.
b) When a particle rotates in a circle, a force acts on it directed toward the center of rotation.
Why is it that, this force does not work on the particle?
Answer: Since at any point along the circle the centripetal force is perpendicular to the velocity
v and therefore to the displacement DR, the scalar product DW = F·DR is zero therefore this
force does not work on it.
