Question

Question 60:
A man wearing a bullet-proof vest stands still on roller skates. The total mass is 80 kg. A bullet of mass 20 grams 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 ?

Lakhmir Singh Physics Class 9

Answer 1

Answer:

0.1 m/s

Explanation:

Mass of the man = m1 = 80kg (Given)

Mass of bullet = m2 = 20 g = 0.02kg (Given)

Let speed of the man be = v1

Speed of the bullet = v2 = 400 m/s (Given)

Therefore,

According to the law of conservation of momentum -

m1v1 = m2v2

= 80 × v1 = 0.02 × 400

v1 = 400 × 0.02/ 80

v1 = 0.1

Therefore, the velocity of the man is 0.1 m/s.

Answer 2

Dear Student,

◆ Answer -

vm = 0.1 m/s

● Explanation -

# Given -

Mm = 80 kg

Mb = 20 g = 0.02 kg

um = 0 m/s

ub = 400 m/s

vb = 0 m/s

# Solution -

By law of conservation of momentum,

Mm.um + Mb.ub = Mm.vm + Mb.vb

80×0 + 0.02×400 = 80×vm + 0.02×0

8 = 80×vm

vm = 8/80

vm = 0.1 m/s

Therefore, velocity of the man is 0.1 m/s in direction of bullet.

Thanks dear...