Rotational Motion 3

Rotational Motion 3

Multiple Choice

The angular momentum equation for a point mass about a given axis of rotation :

• $L=mvr$

• $L=mvr^2$

• $L=mr^2$

• $L=\frac{mv}{r}$

Multiple Choice

A spinning bike wheel is held horizontally and it is observed to slow down. Why does this not break the law of conservation of angular momentum?

• Friction causes a torque. Torque causes a change in angular momentum

• It does break the law

• Weight causes a torque to be applied which changes the angular momentum

Fill in the Blanks

Multiple Choice

Rotational Energy Equation:

Recall E_k = ½ mv² What is the equation for rotational kinetic energy?

• $E_{kr}=\frac{1}{2}I\omega^2$

• $E_{kr}=\frac{1}{2}I\alpha^2$

• $E_{kr}=\frac{1}{2}\alpha I^2$

• $E_{kr}=\frac{1}{2}\omega I^2$

Multiple Choice

Farica slows a spinning turntable (solid disc) by holding her finger against the edge.

(I = 0.80 kgm² radius = 20 cm. Tangential force = 2.0 N )

The turntable goes from 5.0 rad/s to rest in 10 s.

Calculate the work done by her finger

• 10 J

• 5.8 J

• 12.5 J

• 25 J