Can you explain the concept? The Answer are D, D and B. The figure at right show

Question

Can you explain the concept? The Answer are D, D and B.

The figure at right shows a potter's wheel rotating about a fixed axis in the counter-clockwise direction. Assume the wheel is rotating at a fixed rate (no friction and no motor). Points P and Q are at two different points on the wheel; point P is closer to the axis than point Q. Which of the following statements about points P and Q is correct? A. Point P has greater angular speed than point Q B. Point P has smaller angular speed than point Q C. Point P has greater linear speed than point Q D. Point P has smaller linear speed than point Q E. None of the above statements is correct Suppose that the potter exerts a constant torque on the wheel such that the wheel begins to slowdown. Which of the following best describes the direction of the net torque applied to the wheel while it is slowing down? A. Counter-clockwise B. Clockwise C. Vertically upward along the axis of rotation D. Vertically downward along the axis of rotation E. Too complicated to describe by a single vector since each particle has a different motion The wheel slows down uniformly, then begins to speed up uniformly in the opposite direction. Consider the instant t when the wheel is instantaneously at rest. At the instant t, which of the following quantities are nonzero? A. Angular velocity B. Angular acceleration C. Angular momentum D. All of the above quantities (A, B, C) are nonzero E. None of the above quantities (A, B, C) are nonzero

Explanation / Answer

25. angular speed will be same for all the points .

but linear speed = w r

Q has greater r hence it will have greater linear speed.

Ans(D)

26.

angular acceleration have to be in opposite direction of angular speed to slow down.

hence torque will be vertical downward.

Ans(D)

27. at t. at rest hence angular speed will be zero.

and at t, angular acceleration is non-zero.

and angular momentum = I w

so angular momentum will also be zero

Ans(B)

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