Question

A ball of mass x kg and speed y m/s, moves towards a wall and after a
perfectly elastic collision starts moving exactly in the opposite direction with
same speed. Find the change in momentum. ​

Answer 1

Concept:

During elastic collision, two important points occur:

1. momentum remain conserved (external force is zero).
2. energy of the system is conserved(zero energy loss).

Solution:

First, draw the fig. as per the question and mark all normal forces.

According to question,

$\rm V_{seperation}=V_{approach}= V= y$

• Initial momentum of ball = my(- î) = – xy î

• final momentum of ball = mv î = xy î

Change in momentum = final - initial

• xy î - (-xy î) = (xy + xy) î
• 2xy î

★ So, change in momentum of ball is 2xy and in positive x-direction.