Question

A man of mass 60 kg and a boy of mass 30 kg are standing together on a frictionless ice surface. If they push each other apart, the man moves away with a speed of 0.4m/s relative to ice. After 5s they will be away from each other at a distance of ___________

(a) 9 m

(b) 3 m

(c) 6 m

(d) 30 m

I have been asked this question in examination.

The question is from Laws of Nature topic in portion Laws of Motion of Engineering Physics I

Answer 1

Right choice is (c) 6 m

Easy explanation: Momentum of man = -Momentum of boy

60×0.4 = -30×v

Velocity of the boy = -0.8m/s

Relative velocity = 0.4+0.8 = 1.2m/s

Distance between man and boy after 5s = 1.2×5 = 6 m.