A particle of mass M is moving in a horizontal circle of radius R with uniform speed v. When it moves from one point to a diametrically opposite point, its?

A.

Kinetic energy changes by (Mv)^{2}/4

B.

Momentum does not change

C.

Momentum changes by 2Mv

D.

Kinetic energy changes by (Mv)^{2}

Answer: Option C

Explanation:

At any two diametrically opposite points, velocities of the particle have the same magnitude but opposite directions. Therefore change in momentum = Mv-(-MV)=2Mv.

Two identical balls A and B collide head on elastically. If velocities of A and B, before the collision are +0.5m/s and -0.3m/s respectively, then the velocities after the collision, are?

A.

-0.5m/s and +0.3m/s

B.

+0.5m/s and +0.3m/s

C.

+0.3m/s and -0.5m/s

D.

-0.3m/s and +0.5m/s

Answer: Option D

Explanation:

In an elastic collision between two bodies of equal masses, velocities get exchanges after collision. v_{A}=-0.3m/s and v_{B}=+0.5m/s.