Question

A rifle of mass 2 kg fires a bullet of mass 20 g with velocity of 150 m/s. Because of this, the gun is pushed back with a velocity of
(a) 1500 m/s
(b) 1.5 m/s
(c) 15 m/s
(d) -1.5 m/s​

Answer 1

Answer:

The gun is pushed back with a velocity of 0.66 m/s.

Explanation:

Given:

• Mass of rifle = 2kg
• Mass of bullet = 20g
• Velocity = 150 m/s

To Find:

• Velocity by which gun is pushed back = ?

Solution:

Velocity by which gun is pushed back = ?

Momentum = mass × velocity

Momentum before gun is fired = momentum of gun after fired + momentum of gun before fired.

Consider velocity of gun as ‘v’ m/s.

Bullet of mass = 20g = 0.02kg

By conservation of momentum,

=> m1v1 + m2v2

=> (2kg + 0.02kg) × 0 = (2kg × v m/s) + (0.02kg × 150 m/s)

=> 0 = 2v + 3

=> v = 2/3

=> v = 0.66 m/s

∴ Gun is pushed back with a velocity of 0.66 m/s.