Question

A smooth sphere A is moving on a frictionless horizontal plane with angular speed ω and the centre of mass velocity u. It collides elastically and head on with an identical sphere B at rest. Neglect friction everywhere. After the collision, their angular speeds are ω(A) and ω(B) respectively. Then?

(a) ωA is lesser than ωB

(b) ωA=ωB

(c) ωA=ω

(d) ωB=ω

Answer 1

Right answer is (c) ωA=ω

Explanation: Only their linear velocities are exchanged. The two spheres cannot exert torques on each other, as their surfaces are frictionless, and so that angular velocities of the sphere do not change.