How Is Amplitude and Total Energy Calculated in a Spring System?

[hangten1039]

A mass of 0.5 kg is attached to the end of a massless spring of spring constant 0.40 N/m. It is released from rest from an extended position. After 0.7 s, the speed of the mass is measured to be 1.75 m/s. What is the amplitude of oscillation? What is the total energy (relative to the mass at rest in the unextended position) contained in this system?



x=Acoswt
conservation of energy



I've tried many different attempts.

 

[hangten1039]

Anyone have any help on this problem. I think I have to use conservation of energy but I really am not sure