Q: A smooth sphere A is moving on a frictionless horizontal plane with angular velocity ω and centre of mass velocity v. It collides elastically and head on with an identical sphere B at rest. Neglect friction everywhere. After the collision their angular speeds are ωA and ωB respectively. Then,
(a)ωA < ωB
(b)ωA = ωB
(c) ωA = ω
(d)ωB = ω
Ans: (c)
Sol: Since , there is head on elastic collision between two identical spheres , hence they will exchange their velocities i.e. A comes to rest and B starts moving with linear velocity v . As there is no friction anywhere , torque on both the sphere about their centre of mass is zero & their angular velocities remains constant .
ωA = ω & ωB = 0