Question

A variable mass body with an initial mass of 5 kg is moving with a velocity of 5 m/s initially, after some time the velocity increases to 10 m/s, what is the new mass if the body is moving in the absence of any external force?

(a) 2.5 Kg

(b) 5 Kg

(c) 7.5 Kg

(d) 10 Kg

I have been asked this question during a job interview.

I would like to ask this question from Laws of Motion topic in portion Laws of Motion of Physics – Class 11

Answer 1

The correct choice is (a) 2.5 Kg

For explanation I would say: The body is moving in the absence of any external force thus the momentum remains conserved.  m1v1 = m2v2. v1 = 5 m/s, m1 = 5 Kg, v2 = 10 m/s. On solving, we get, m2 = 2.5 kg. Hence, the correct answer is 2.5 Kg.