Question

A $12kg$ bomb at rest explodes into two pieces of $4kg$ and $8kg$. If the momentum of $4kg$ piece is $20Ns$, the kinetic energy of the $8kg$ piece is:

• A. $25J$
• B. $20J$
• C. $50J$
• D. $40J$

Answer 1

The correct option is A $25J$

As initial momentum of the system is zero. Thus according to law of conservation of momentum, final momentum of the system must also be zero.

Hence momentum of $8kg$ piece must be equal and opposite to the momentum of $4kg$ piece.

$⟹$ Momentum of $8kg$ piece, $P=20Ns$

Kinetic energy of $8kg$ piece, $K=\frac{P^2}{2m}=\frac{{20}^2}{2\times 8}=25$ $J$