Chapter 12: Q. 20 (page 331)
The 20-cm-diameter disk in FIGURE EX12.20 can rotate on an axle through its center. What is the net torque about the axle?

Short Answer
The net torque on the axle is , the direction is clockwise.
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Chapter 12: Q. 20 (page 331)
The 20-cm-diameter disk in FIGURE EX12.20 can rotate on an axle through its center. What is the net torque about the axle?

The net torque on the axle is , the direction is clockwise.
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The two blocks in FIGURE CP12.86 are connected by a massless rope that passes over a pulley. The pulley is 12 cm in diameter and has a mass of 2.0 kg. As the pulley turns, friction at the axle exerts a torque of magnitude 0.50 N m. If the blocks are released from rest, how long does it take the 4.0 kg block to reach the floor?

In FIGURE CP12.88, a 200 g toy car is placed on a narrow 60-cm-diameter track with wheel grooves that keep the car going in a circle. The 1.0 kg track is free to turn on a frictionless, vertical axis. The spokes have negligible mass. After the car’s switch is turned on, it soon reaches a steady speed of 0.75 m/s relative to the track. What then is the track’s angular velocity, in rpm?

FIGURE CP12.89 shows a cube of mass m sliding without frictionat speed v0. It undergoes a perfectly elastic collision with the bottom tip of a rod of length d and mass M = 2m. The rod is pivoted about a frictionless axle through its center, and initially it hangs straight down and is at rest. What is the cube’s velocity— both speed and direction—after the collision?

An 18-cm-long bicycle crank arm, with a pedal at one end, is attached to a 20-cm-diameter sprocket, the toothed disk around which the chain moves. A cyclist riding this bike increases her pedaling rate from 60rpm to 90 rpm in 10s .
a. What is the tangential acceleration of the pedal?
b. What length of chain passes over the top of the sprocket during this interval?
How fast, in rpm, would a diameter bowling ball have to spin to have an angular momentum of ?
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