Posted by Jake on .
An object with mass 0.250 kg is acted on by an elastic restoring force with force constant 10.8 N/m. The object is set into oscillation with an initial potential energy of 0.150 J and an initial kinetic energy of 6.00×10−2 J.
What is the amplitude of oscillation?
What is the potential energy when the displacement is onehalf the amplitude?
At what displacement are the kinetic and potential energies equal?
What is the value of the phase angle \phi if the initial velocity is positive and the initial displacement is negative?

Physics 
drwls,
(1/2) k x^2 + (1/2)mV^2 = 0.21 J
= total energy = constant
Set V = 0 to solve for the amplitude, since V = 0 then
When displacement is half the amplitude, potential energy is 1/4 of the total, 0.1575 J
When KE = PE,
(1/2) kx^2 = 0.015 J. Solve for x at that time
The phase angle depends upon what you call zero phase. Yopu haven't said