Question

1) A uniform 14 kg cylinder turns on a horizontal axis with a significant amount of friction. The cylinder has a radius of 0.030 m and a thickness of 0.080 m. It is initially at rest. Then a force of 70 N is applied at a 37 angle for 2.0 s, as indicated in the figure, and the cylinder accelerates. After a time of 2.0 s the force is reduced to 24 N, and then the cylinder continues to spin at constant angular speed.

a) Calculate the magnitude of the torque acting on the cylinder due to friction.

b) Calculate the angular velocity of the cylinder after 2.0 s.

c) Calculate the cylinder’s kinetic energy after 2.0 s.

37° F

2) A 25 kg child stands 2.5 m from the center of a frictionless merry‐go‐round, which has a 200 kg m2 moment of inertia and is spinning with one revolution every two seconds. The child then moves inward to a radius of 1.5 m.

a) What is the initial angular velocity of the merry‐go‐round?

b) What is the new angular velocity of the merry‐go‐round, after the child moves?

c) By how much did the kinetic energy of the merry‐go‐round increase? Where did this energy come from?

Answer 1

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