9702/May Jun/13/2015/Q19

When a horizontal force F is applied to a frictionless trolley over a distance s, the kinetic energy
of the trolley changes from 4.0 J to 8.0 J.

If a force of 2F is applied to the trolley over a distance of 2s, what will the original kinetic energy
of 4.0 J become?

A 16 J
B 20 J
C 32 J
D 64 J

Solution:

Answer: B.

Initial kinetic energy of trolley = 4J

Consider the 1^st case.

We need to consider the initial 4J here.

Final kinetic energy = 8J

Work done by force F (= Fs) = 8 – 4 = 4J

So, Fs = 4J

Consider the 2^nd case.

Work done by force 2F = (2F) (2s) = 4(Fs) = 4(4) = 16J since Fs = 4J

Total kinetic energy = 4 + 16 = 20J

Reference: PYQ - May/Jun 2015 Paper 13 Q19