Question

A variable mass body with an initial mass of 10 kg is moving with a velocity of 7 m/s initially, after some time the velocity increases to 14 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 had been asked this question in an interview.

Asked question is from Laws of Motion topic in portion Laws of Motion of Physics – Class 11

Answer 1

Correct option is (b) 5 Kg

The best explanation: The body is moving in the absence of any external force thus the momentum remains conserved. m1v1 = m2v2. v1 = 7 m/s, m1 = 10 Kg, v2 = 14 m/s. On solving, we get, m2 = 5 kg. Hence, the correct answer is 5 Kg.