Question

A ball moving at a speed of $3\text{m/s}$ approaches a wall moving towards it with a speed of $3\text{m/s}$. After the perfectly elastic collision, the speed of the ball will be

• A. $3\text{m/s}$
• B. $6\text{m/s}$
• C. $9\text{m/s}$
• D. $0$

Answer 1

The correct option is C $9\text{m/s}$

Since, the wall is considerably heavier than ball therefore, velocity of wall will not change.
Let speed of ball after collision is $V$


Now, for perfectly elastic collision,
speed of approach = speed of separation
$3-(-3)=V-3\Rightarrow 6=V-3\Rightarrow V=9\text{m/s}$