### NEET Solved Paper 2019 Question 5

##### Question: Body A of mass 4m moving with speed u collides with another body B of mass 2m, at rest. The collision is head on and elastic in nature. After the collision the fraction of energy lost by the colliding body A is: [NEET 5-5-2019]

#### Options:

A) $ \frac{4}{9} $

B) $ \frac{5}{9} $

C) $ \frac{1}{9} $

D) $ \frac{8}{9} $

## Show Answer

#### Answer:

Correct Answer: D

#### Solution:

$ v _2=\frac{m _1+u _1+u _2(m _2-m _1)}{m _1+m _2} $

$ v _2=\frac{2(4m)u+0}{6m} $

$ v _2=\frac{4}{3}u $

$ \frac{\Delta E}{E}=\frac{\frac{1}{2}2mv_2^{2}}{\frac{1}{2}4mu^{2}}=\frac{{{( \frac{4}{3}u )}^{2}}}{2u^{2}}=\frac{8}{9} $