The momentum of a bullet of mass $20\ g$ fired from a gun is $10\ kg.m/s$. The kinetic energy of this bullet in $kJ$ will be:
(a) 5
(b) 1.5
(c) 2.5
(d) 25

Here, the mass of the bullet $m=20\ g=\frac{20}{1000}\ kg$
 

Momentum of the bullet $mv=10\ kg.m/s$  [$v$ is the velocity of the gun.]

$\frac{1}{500}\times v=10\ kg.m/s$

Or $v=5\times10^3$

Therefore, the kinetic energy of the bullet $K=\frac{1}{2}mv^2$

Or $K=\frac{1}{2}\times\frac{1}{500}\times(5\times10^3)^2$

Or $K=25\times 10^3\ J$

Or $K=25\ KJ$

Therefore, option (d) is correct.

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Updated on: 10-Oct-2022

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