Energy Principle - Engineering Physics - Lecture Slides, Slides of Engineering Physics

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The Energy Principle

W = F · dr = F · ∆r

= Fx∆x + Fy ∆y + Fz ∆z

Ef − Ei = Wsurr + other energy transfers

A block accelerates down a frictional inclined plane that is at an angle θ with respect to the horizontal. Choose the x-axis to be positive up along the plane (so a < 0).

Draw and label a free body diagram. How much work is done by friction as the box slides down the plane a

distance D from where it was released?

1. Wf = μk m g D sin θ

2. Wf = μk m g D cos θ

3. Wf = −μk m g D sin θ

4. Wf = −μk m g D cos θ

5. Wf = μk m g D tan θ docsity.com

1. D A = D B

2. D A = 2 D B

3. DA = 4 D B

4. DB = 4 D A

5. DB = 2 D A

Object A with mass 4 kg moves at an initial speed of 2 m/s along a frictionless horizontal plane. A horizontal force F is applied opposite to the direction of the motion and brings object A to a stop in a distance DA.

Object B with mass 2 kg moves at an initial speed of 4 m/s along the frictionless horizontal plane. The same horizontal force F is applied opposite to the direction of the motion of B and brings object B to a stop in a distance DB.

What is the relation between D (^) A and D (^) B?

1. 32.5 J

2. 130 J

3. -130 J

4. -32.5 J

5. -65 J

A force is given by F(x) = -Ax 3 , where A= 2 N/m^3 and the units of the force is Newtons. The force F(x) pushes an object from x = -3 m to x = +2 m.

What is the work done by the force F(x)?

1. 0 J

2. 100 J

3. 200 J

4. -100 J

5. -200 J

A spring of equilibrium length L 0 =5 m and spring constant k=10 N/m is laying on a frictionless table with the left end attached to the table at x=0 m. It pushes a block of mass m=3 kg as the end of the spring moves from x=3 m to x=7 m. How much work did the spring do on the block?

s=-2 m s=+2 m

L 0 =5 m docsity.com