Physics · WORK, ENERGY AND POWER

An ideal massless spring of force constant \( k \) is attached to a rigid wall and rests on a smooth horizontal surface. When the spring is pulled outwards to an extension \( x_m \), the work done by the spring force \( W_s \) is:

1. A
   \( +\frac{1}{2}kx_m^2 \)
2. B
   \( -kx_m \)
3. C
   \( -\frac{1}{2}kx_m^2 \)
4. D
   \( +kx_m^2 \)