Practice!

Sample Problem

Jason launches a model rocket with a mass of 1.2 kg from his spring-powered rocket launcher with a spring constant of 800. N/m. He pulls the spring back .55 m. If Jason aims it straight up, what potential energy will the rocket have when it reaches 3.0 m? What will its kinetic energy be?

J, J

Solution

Us = ½ (k) x2 = 1/2 (800) (.552) = 121

We can use the equation GPE = mgh, so we are given m = 1.2, and h = 3.0 and we know that g ≈ 9.81, so GPE = (1.2) (3) (9.81) = 35J

Therefore, KE = 86 J