Question

Two bodies of masses 5 kg and 3 kg are moving towards each other at velocities of 3 m/s and 5 m/s, respectively. What is the velocity of their centre of mass?

(a) 0.25 m/s towards 3 kg

(b) Upredictable

(c) The centre of mass is stationary

(d) 0.5 m/s towards 5 kg

The question was asked in an interview for job.

I would like to ask this question from System of Particles topic in chapter System of Particles and Rotational Motion of Physics – Class 11

Answer 1

The correct option is (c) The centre of mass is stationary

To explain I would say: The velocity of the centre of mass = (m1*v1 + m2*v2)/(m1 + m2)

m1 = 5kg

m2 =3 kg

v1 = 3 m/s

v2 = -5 m/s [opposite direction)

Velocity of centre of mass = (5*3 – 3*5)/(5+3)

 = 0.