Question

A ball is moving with velocity $5\text{m/s}$ towards a heavy wall which is at rest as shown in figure. Assuming collision to be perfectly elastic, find the velocity of the ball immediately after the collision.

• A. $5\text{m/s}$ towards left
• B. $0\text{m/s}$ towards left
• C. $5\text{m/s}$ towards right.
• D. $\frac{5}{2}\text{m/s}$ towards left.

Answer 1

The correct option is A $5\text{m/s}$ towards left

Given, mass of the ball $\left(m_1\right)$ is very less as compared to the mass of the wall $\left(m_2\right)$
Speed of ball before collision $\left(u_1\right)=5\text{m/s}$
Speed of wall before collision $\left(u_2\right)=0\text{m/s}$
Let speed of ball after collision $\left(v_1\right)=v\text{m/s}$
Speed of wall after collision $\left(v_2\right)=0\text{m/s}$
In case of elastic collision, when $m_1<<m_2$
$v_1=-u_1+2u_2$
$\Rightarrow v=-5+0=-5\text{m/s}$
i.e velocity of ball is $5\text{m/s}$ towards left.