$21)$You attach one end of a spring with a force constant $k=793\frac{N}{m}$ to a wall and the other end to a mass $m=2\mathrm{.}62kg$ and

set the mass$-$spring system into oscillation on a horizontal frictionless surface as shown in the figure. To put the system

into oscillation, you pull the block to a position $x_i=6\mathrm{.}76cm$ from equilibrium and release it$.$

$($a$)$ Determine the potential energy stored in the spring before the block is released.

$$

$($b$)$ Determine the speed of the block as it passes through the equilibrium position.

$\frac{m}{s}$

$($c$)$ Determine the speed of the block when it is at a position $\frac{x_i}{4}.$

$\frac{m}{s}$