Practice!

Sample Problem

Johnny stretches a spring 40 cm from its resting position. The spring’s constant of proportionality is 20 N/m. What is the spring potential energy?

J

Solution

We can use the formula US = 1/2 kx2. We will plug in all the values given to us to get

US = 1/2 (20) (.4) 2 = 1.6 J. Notice that we converted 40 cm to .4 m. You must do that in order to make sure all units work together properly.