# 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 (a) 1/9 (b) 8/9 (c) 4/9 (d) 5/9

Fractional loss of KE of colliding body,

$\frac{\Delta&space;KE}{KE}&space;=&space;\frac{4&space;\times&space;(m_{1}m_{2})&space;}{(m_{1}+m_{2})^{2}}$

On substituting the values of m1 and m2, we get,

$=&space;\frac{4\times&space;(4m)&space;\times&space;2m}{(4m&space;+&space;2m)^{2}}$

$=&space;\frac{32m^{2}}{36m^{2}}$

We get,

$=&space;\frac{8}{9}$

Therefore, the correct option is (b)