Question

A charged body is kept in an electric field where it experiences a constant acceleration of 10 m/$s^2$ in the positive x-direction. The body hits wall after travelling 4 m and rebounds but can travel only upto 2 m before coming to rest momentarily . If the body was in contact with the wall for 12 ms then find the average acceleration of it due to the impact?

• A.
• B.
• C.
• D.

Answer 1

The correct option is D

Let's break the motion into 2 chunks

1. $\underset{–}{ForwardMotion}$

u = 0 $a=+10m/s^2$

v= v m/s

s = + 4m so $v^2=u^2+2as$

$v=\sqrt{80}m/s$

$\underset{–}{BackwardMotion}$

Let Initial velocity = u v = 0

$\therefore$ ball is stopping

a = 10 m/$s^2$

s = -2m since in negative x direction

$v^2-u^2=2.10(-2)$

$u^2=40$

$u=\pm \sqrt{40}m/s$

We know u will be negative as particle after collision starts moving in negative direction.

So $u=-\sqrt{40}m/s$

So during collision period ball came with $v=+\sqrt{80}m/s$

after $12\times {10}^{-3}s$

Ball rebounded back with v = $-\sqrt{40}m/s$

$a=\frac{-\sqrt{40}-\sqrt{80}}{12\times {10}^{-3}}$

$a=-1.2\times {10}^{3}m/s^2$

Negative sign says that the particles average acceleration during collision was in negative x-direction.