Question

A bomb of mass 30 kg at rest explodes into two pieces of masses 18 kg and 12 kg. The velocity of 18 kg mass is 6 ms${}^{-1}$. The kinetic energy of the other mass is :

• A. 324 J
• B. 486 J
• C. 256 J
• D. 524 J

Answer 1

The correct option is B 486 J

Momentum is conserved just before and after the explosion of the bomb.
Initial momentum is zero, so the resultant momentum of the exploded pieces should be zero.
That is $m_1{v}_1=m_2{v}_2$

$\Rightarrow \left(18\right)\left(6\right)=12\left(v_2\right)$

$\Rightarrow v_2=9m/s$

$\therefore$ the KE of 12kg mass$=\frac{1}{2}12\left(9^2\right)=486J$