Question

The kinetic energy of a body is ‘K’. If one-fourth of its mass is removed and velocity is doubled, the new kinetic energy will be _____

(a) K

(b) 3K

(c) 4K

(d) 9K/4

I have been asked this question in a national level competition.

This question is from Kinetic Energy topic in division Work, Energy and Power of Physics – Class 11

Answer 1

Right option is (b) 3K

The best explanation: K = 1/2 x m x v^2

New kinetic energy (K’) = 1/2 x m’ x v’^2

m’ = 3m/4; [one-fourth of mass is removed]

v’ = 2v; [velocity is doubled]

K’ = 1/2 x (3m/4) x (2v) ^2

 = 1/2 x m x v x 3

 = 3 x K

 = 3K.