Question

A smooth sphere $A$ is moving on a frictionless horizontal plane with angular speed $\omega$ 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 ${\omega }_A$ and ${\omega }_B$, respectively. Then

• A. ${\omega }_A<{\omega }_B$
• B. ${\omega }_A={\omega }_B$
• C. ${\omega }_A=\omega$
• D. ${\omega }_B=\omega$

Answer 1

Answer: (C)

${\omega }_A=\omega$

Since the spheres are smooth, there will be no transfer of angular momentum from the sphere $A$ to sphere $B$. The sphere $A$ only transfers its linear velocity $v$ to the sphere $B$ and will continue to rotate with the same angular speed $\omega$.