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.