Q20 of 49 Page 9

From a rifle of mass 4 kg, a bullet of mass 50 g is fired with an initial velocity of 35 m s-1. Calculate the initial recoil velocity of the rifle.

Firstly, we will calculate the momentum of both rifle and bullet separately.

Momentum of bullet = Mass of bullet × Velocity of bullet 

As we know that p= m × v

Putting the values in above equation we get:-


= 0.05 kg × 35 m/s   (As 1 kg=1000 gram)

= 1.75 kg m/s (i)


Similarly we solve for momentum of rifle

Momentum of rifle = Mass of rifle × Velocity

Putting the value in above equation we get:-

= 4 kg × v m/s

= 4v kg m/s
We know that,

According to the law of conservation of momentum:

Momentum of bullet = Momentum of rifle

1.75 = 4v [From (i) and (ii)]


v =


v = 0.4375 m/s


Therefore, the recoil velocity of the rifle is 0.4375 m/s

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