Worked Example

Problem:
A spring with $k = 100 \, \text{N/m}$ is stretched by $0.1 \, \text{m}$. Find energy stored.

Solution

$$ U = \frac{1}{2}kx^2 = \frac{1}{2} \times 100 \times 0.01 = 0.5 \, \text{J} $$