A turntable with rotational inertia spins counter-clockwise at an angular speed of

PHYSICS · Multi-part · AP · Physics 1: Algebra-based · Energy and Momentum of Rotating Systems · Energy and Momentum of Rotating Systems

Problem

A turntable with rotational inertia

I = 0.25\,\text{kg}\!\cdot\!\text{m}^2

spins counter-clockwise at an angular speed of

4.0\,\text{rad}\!/\text{s}

. Two separate torques act on the turntable in sequence: • First, a kinetic-friction torque of

0.40\,\text{N}\!\cdot\!\text{m}

(clockwise) acts for

2.0\,\text{s}

. • Immediately afterward, an external motor supplies a constant

0.60\,\text{N}\!\cdot\!\text{m}

counter-clockwise torque for

1.0\,\text{s}

. Ignore any other torques. (a) Compute the angular impulse delivered by the friction torque. (b) Determine the angular speed of the turntable just after the friction torque ceases. (c) Compute the angular impulse delivered by the motor. (d) Calculate the final angular speed of the turntable after both torques have acted. State the direction of rotation.

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