Physics
posted by Jimmy .
A 0.53kg mass is attached to a horizontal spring with k = 106 N/m. The mass slides across a frictionless surface. The spring is stretched 27 cm from equilibrium, and then the mass is released from rest.
(a) Find the mechanical energy of the system.
(b) Find the speed of the mass when it has moved 9 cm.
(c) Find the maximum speed of the mass.

a) ME= 1/2 k x^2
b) 1/2 m v^2=change in PE= 1/2 k (.27^2.09^2) 
In turns out that for b), instead of using
(.27^2 0.09^2), we have to use (.27^20.18^2). 
I think your solution tells us when the spring moves 18 cm, not 9 cm.
Thank you, though. This was really useful.