Two-dimensional oscillator. A particle is free to move in the $x, y$ plane under the action of a force toward the origin of magnitude $-C(x \hat{\mathrm{x}}+y \hat{y})=-C r$. Assuming the mass is $M$, find the $x$ and $y$ equations of motion and solve them.
(a) What are the conditions for motion in a circle and what is the period?
(b) What are the conditions for motion along the line at $45^{\circ}$ to the $x$ axis and what is the period?