A disk with a mass of 18 kg, a diameter of 25 cm, and a thickness of 8 cm is mou

Question

A disk with a mass of 18 kg, a diameter of 25 cm, and a thickness of 8 cm is mounted on a rough horizontal axle as shown on the left in the figure. (There is a friction force between the axle and the disk.) The disk is initially at rest. A constant force, F = 70 N,is applied to the edge of the disk at an angle of 37°,as shown on the right in the figure. After 2.0 s, the force is reduced to F = 22 N,and the disk spins with a constant angular velocity.


(a) What is the magnitude of the torque due to friction between the disk and the axle?


(b) What is the angular velocity of the disk after 2.0 s?


(c) What is the kinetic energy of the disk after 2.0 s?

Explanation / Answer

net torque = I

(70.0N)(sin 37)(0.125m) - 1.654 N m = (0.140 kg m2 )

thus = 25.79 rad/sec2 .

The rotational kinematics eqn is f = i + t

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