A moving railway compartment has a spring of constant k fixed to its front wall. A boy stretches this spring by distance x and in the mean time the compartment moves by a distance s. The work done by boy w.r.t. earth is

Options

A. (a) `1/2kx^2`
B. (b) `1/2(kx)(s+x)`
C. (c) `1/2kxs`
D. (d) `1/2kx(s+x+s)`

Answer

A

Explanation

Total work done in equal to the energy stored in the spring.