6.6.2 Torque and Angular Momentum

Question 1

The derivative of the equation L = r x p is
dL/dt = (dr/dt) x p + r x (dp/dt)
Which of the following states why the term dr/dt x p always vanishes?

Answer 1

dr/dt and p are always in the same direction

Question 2

For a system of many particles, which of the following contributes to the net torque?

Answer 2

external torques only

Question 3

For a bicycle wheel that experiences zero external torque, which of the following is true?

Answer 3

the angular acceleration is always zero

Question 4

Which of the following equations is not a rotational analog to Newton’s second law?

Answer 4

t = r x F

Question 5

The statement dL/dt = rx F is not true for

Answer 5

this equation is always true

Question 6

Two objects are pulling each other with an action-reaction force as shown in the diagram. With respect to the origin shown, what is the torque action in object A compared to the torque acting on object B

Answer 6

tA = tB

Question 7

Consider a rotating bicycle wheel and the torque due tot he friction acting on it. Which of the following effects is not due to this torque?

Answer 7

the term dL/dt will be greater than zero

Question 8

An object is constrained to rotate in the xy-plane around a rigid massless rod, as shown in the diagram. In which of the following directions should a torque be applied in order to increase the angular momentum?

Answer 8

along the positive z-axis

Question 9

If the external torque acting on a bicycle wheel is zero, which of the following statements is always true?

Answer 9

The angular momentum of the wheel is constant