posted by jane .
A 0.21 kg block oscillates back and forth along a straight line on a frictionless horizontal surface. Its displacement from the origin is given by
x = (16 cm)cos[(16 rad/s)t + π/2 rad]
What force, applied to the block by the spring, results in the given oscillation?
why can you not just do F=ma?
Yes. This is a duplicate post. I answered it elsewhere