Question

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

• A. $\frac{1}{2}k{x}^2$
• B. $\frac{1}{2}\left(kx\right)(s+x)$
• C. $\frac{1}{2}kxs$
• D. $\frac{1}{2}\left(kx\right)(s+x+s)$

Answer 1

The correct option is A $\frac{1}{2}k{x}^2$

By energy conservation,

work done by boy=store energy in spring$=\frac{1}{2}k{x}^2$