AP Physics 1 5.3.A: Torques on a Rigid System

Practise AP Physics 1 5.3.A by deciding whether forces on beams, disks, and orbiting objects produce torque about a chosen pivot or rotation axis.

Exam points

Decide whether a force on a beam or disk exerts torque by tracing its line of action to the pivot.
Explain zero torque for a radial force and nonzero torque from a component perpendicular to r.

[Maximum number: 1]

8 points; suggested time: 15-20 minutes

A mass m is initially resting at the center of a rotating disk with

rotational inertia $(1 / 2) M R^{2}$ . The entire system is freely rotating with an

initial angular speed of $w_{0}$ . As time goes by, the mass is carefully

moved at a constant speed outward from the center. This is done in

such a way that no torque on the system is introduced.

(b) How can one push the small mass m such that no torque is

induced?

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