An elastic wire suspended from a workbench has a 2kg mass attached to its free end. The wire changes in length by 2cm. Calculate the elastic potential energy stored in the wire.

Using Hooke's law (F = k * e) we can find the spring constant. Rearranging for k, we find that k = (9.81 * 2)/0.02 = 981 N/m. To calculate this we needed to find the force acting on the wire (F = mg) and also convert our extension into meters. In a session I would draw a diagram of the system showing the forces acting and the extension of the wire.We can then substitute this into the equation for elastic potential energy: E = 0.5 * k * e^2 = 0.196 J.