AP Physics C: Mechanics 6.3.C: Angular Impulse

Practise relating angular impulse to changes in angular momentum by using a disk’s rotational inertia, final angular speed, and contact time.

Exam points

Calculate average torque as ΔL/Δt, using a disk’s rotational inertia and final angular speed.

[Maximum number: 1]

Questions 14-16 A ball of mass 2.0 kg is thrown vertically upward from the top of a building. The ball's velocity v is given as a function of time t by the equation v(t)=R-S t, where $R=5 \mathrm{~m} / \mathrm{s}$ and $S=10 \mathrm{~m} / \mathrm{s}^{2}$ . The positive direction is upward.

18. The interval of time $\Delta t$ is the elapsed time from the moment of first contact between the two disks until they are both spinning at the same angular velocity. Which of the following expressions gives the magnitude of the average torque that the first disk exerts on the second disk?

$M R^{2} \omega_{f}$

$\frac{M R^{2} \omega_{f}}{\Delta t}$

$\frac{M R^{2} \omega_{f}}{2 \Delta t}$

$\frac{2 M R^{2} \omega_{f}}{\Delta t}$

It cannot be determined without knowing the nature of the forces between the two disks.

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6.3.C—Relate the change in angular momentum of an object or rigid system to the angular impulse given to that object… question 1