Question

A perfectly elastic ball of mass $m$ moving with velocity $u$ hits a wall moving with velocity $v$ in the opposite direction. After the collision the ball will rebound back with speed

• A. $u$
• B. $u - v$
• C. $u + 2v$
• D. $u + v$

Answer 1

Answer: (C)

$u + 2v$

Answer 2

Given :
Mass of ball = m
Initial velocity = u
Final velocity = v
Now,
$⇒e=\frac{\text{Veloctiy of seperation}}{\text{Velocity of approach}}$
$⇒1=\frac{v_2-v_1}{u_2-u_1}$
$1=\frac{v_0-v}{u+v}$
⇒ u + v = v0 - v
⇒ v0 = u + 2v
So, the correct option is (C) : u + 2v.