A 5 Kg marble is fired vertically upward using a spring gun. The spring must be compressed 8.0cm if the marble is to just reach a target 20m above the marble’s position on the compressed spring.

Question

A 5 Kg marble is fired vertically upward using a spring gun. The spring must be compressed 8.0cm if the marble is to just reach a target 20m above the marble’s position on the  compressed spring.
a)	What is the change ∆U in the gravitational potential energy of the marble-Earth system during the 20m ascent? 
b)	What is the change in ∆U in the elastic potential energy of the spring during its launch of marble?
c)	What is the spring constant of the spring?

drwls · Answer

I am sure that you know by now the formulas for gravitational potential energy and the potential energy of a compressed spring. The two P.E.s are equal in this case.