Question

A moving body of mass m and velocity 3km/h collides with a rest body of mass 2m and strikes to it. Now the combined mass starts to move. What will be the combined velocity?

(a) 3km/h

(b) 4km/h

(c) 1km/h

(d) 2km/h

This question was posed to me in an international level competition.

My question comes from Relation between Torque and Momentum topic in division System of Particles and Rotational Motion of Engineering Physics I

Answer 1

Right option is (c) 1km/h

The explanation is: By conservation of momentum,

m×3+2m×0=(m+2m)v

v = 1km/h.