Question

1. From a rifle of mass 4 kg, a bullet of mass 50 g is fired with a velocity of 35 m/s. Calcul.
the recoil velocity of the rifle.
2. A man wearing a bullet-proof vest stands on roller skates. The total mass is 80 kg. A
bullet of mass 20 g is fired at 400 m/s. It is stopped by the vest and falls to the ground.
What is then the velocity of the man?
3.
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English (United States

Answer 1

Answer:

Given

Mass of the rifle (m1) = 4 kg

Mass of the bullet (m2) = 50 g = 0.05 kg

Recoil velocity of the rifle = v1

A bullet is fired with an initial velocity (v2) = 35 m/s

Find out

The initial recoil velocity of the rifle.

Solution

Initially, the rifle is at rest.

Thus, its initial velocity (v) = 0

The total initial momentum of the rifle and bullet system

⇒ (m1+m2) × v = 0

The total momentum of the rifle and bullet system after firing

= m1v1 + m2v2

= (4 × v1 ) + (0.05 × 35)

= 4v1 + 1.75

According to the law of conservation of momentum

Total momentum after the firing = Total momentum before the firing

4v1 + 1.75 = 0

v1= -1.75 / 4

v1 = – 0.4375 m/s

The negative sign indicates that the rifle recoils backwards with a velocity of 0.4375 m/s.