Question

A highly elastic ball moving at a speed of 3 m/s approaches a wall moving towards it with a speed of 3 m/s. After the collision, the speed of the ball will be :

• A. 3 m/s
• B. 6 m/s
• C. 9 m/s
• D. zero

Answer 1

The correct option is C 9 m/s

Given: Coefficient of restitution $e=1$

Speed of the wall $u=3$ $m{s}^{-1}$

Velocity of the ball before collision $v=3$ $m{s}^{-1}$

Let the speed of the particle after collision be $v^{\prime }$

Using $\frac{v^{\prime }-u}{-v-u}=-e$

$\frac{v^{\prime }-u}{-v-u}=-1$ $⟹v^{\prime }=v+2u$

$\therefore$ $v^{\prime }=3+2\left(3\right)=9$ $m{s}^{-1}$