The question is:
A spring is hung from a roof. Uncompressed it is 40cm long. The spring is known to have a spring constant of 10Nm-1
A ball of mass 0.2kg is hung from the spring which extends to 60cm. (therefore extension is equal to 20cm)
(Note the ball is stationary not oscillating)
Calculate energy stored in the spring.
Now to solve this is took the change in gravitational potential energy to find the energy absorbed by the spring. Using E=mgh
A friend used the energy of a spring equation which is E=0.5kx^2
The Attempt at a Solution
Using the change in potential energy I produced the answer of 0.4 J
Using the spring equation an answer of 0.2 J
Which is correct? I'm sure one is incorrect because it does not account for gravity or something along those lines but can't think of a way to show it.