Question

From a rifle of mass $4kg$, a bullet of mass $50g$ is fired with an initial velocity of $35m{s}^{-1}$ with respect to the ground. Calculate the initial recoil velocity of the rifle.

• A. 0.3375 m/s
• B. 0.4375 m/s
• C. 0.4 m/s
• D. 0 m/s

Answer 1

The correct option is B

0.4375 m/s

Initial velocity of bullet and rifle is zero

Mass of rifle = 4 kg

Mass of bullet = $\frac{50}{1000}=0.05kg$

Final velocity of bullet = $35m{s}^{-1}$

Final velocity of rifle = $v$

Since momentum is conserved, so initial momentum is equal to final momentum

$(4\times v)+(0.05\times 35)=0$

$v=\frac{(-35\times 0.05)}{4}$

$v=-0.4375m{s}^{-1}$

The negative sign indicates that the rifle recoils with the velocity of $0.4375m{s}^{-1}$ in backward direction.