# Multiple choice questions

by key
Tags: choice, multiple
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 Quote by key A sphere of mass M, radius r, and rotational inertia I is released from rest at the top of an inclined plane of height h as shown above. 1. If the plane is frictionless, what is the speed vcm, of the center of mass of the sphere at the bottom of the incline? (A) (B) (C) (D) (E) I think the answer is A
erm aren't you forgetting something?
 2.. The momentum p of a moving object as a function of time t is given by the expression p = kt3, where k is a constant. The force causing this motion is given by the expression (A) 3kt2 (B) 3kt2/2 (C) kt2/3 (D) kt4 (E) kt4/4 I think the answer is B
Why? Give reasons (and yes, I know the question doesn't ask for them)
 3. A long board is free to slide on a sheet of frictionless ice. As shown in the top view above, a skater skates to the board and hops onto one end, causing the board to slide and rotate. In this situation, which of the following occurs? (A) Linear momentum is converted to angular momentum. (B) Kinetic energy is converted to angular momentum. (C) Rotational kinetic energy is conserved. (D) Translational kinetic energy is conserved. (E) Linear momentum and angular momentum are both conserved. I think the answer is E
Yes.
 4. Two pucks moving on a frictionless air table are about to collide, as shown above. The 1.5 kg puck is moving directly east at 2.0 m/s. The 4.0 kg puck is moving directly north at 1.0 m/s. What is the magnitude of the total momentum of the two puck system after the collision? (A) 1.0 kg•m/s (B) 3.5 kg•m/s (C) 5.0 kg•m/s (D) 7.0 kg•m/s (E) 5.5 kg•m/s I think the answers is D
You've added the total momentum (3 and 4) before the collision.

How do you add momentums? Is it the same after the collision?

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