Rotation Quiz

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A disk of radius 0.5 m rotates about a center axle. The angular position as a function of time for a point on the edge of the disk is shown. Which of the following quantities can be correctly mathematically determined from the graph? Select all correct answers.

• The tangential velocity of a point at the edge of the disk

In each of the pulleys shown below, the mass of the pulleys is the same in each case as are their radii. In one case, the pulley is shaped like a disk, in another a ring with two light (massless) spindles and a third with massive rope wound inside the pulley as shown. Mass of the disk = Mass of the ring = Mass of the ring+massive rope wound inside. Which of the pulley systems has the greatest moment of inertia?

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• All have the same moment of inertia

• Initial kinetic energy of the disk

A uniform rod is hinged at the one end (the dark dot on the left). What is the magnitude and direction of the net torque on the rod?

• 75 mN clockwise

• 75 mN counter clockwise

• 325 mN Counterclockwise

• 325 mN clockwise

• 75 N counter clockwise

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• can not be determined

In an experiment, a student applies a net force to the edge of a disk for 10s. The student may change the magnitude and the direction of the force at any time in the experiment. A graph of the net torque exerted on the edge of the disk as a function of time is shown. After observing the graph, the student concludes that the angular momentum of the disk has not changed. Does the graph support the student’s conclusion? Justify your answer.

• Yes, because the change in the net torque from 0 s to 10 s is zero.

• Yes, because the slope of the curve of the graph from 0s to 5s has the same magnitude but opposite sign as the slope of the curve from 5s to 10s.

• No, because the area bound by the curve and the horizontal axis from 0s to 10s is not zero

• No, because the graph cannot be used to determine how the angular momentum has changed