A horizontal spring attached to a wall has a force constant of$$k$=700$N$/$m$.$ A block of mass$$m$=1\mathrm{.}20$kg$$is attached to the spring and rests on a frictionless, horizontal surface as in the figure below.

$($a$)$ The block is pulled to a position$$xi$=5\mathrm{.}40$cm from equilibrium and released. Find the potential energy stored in the spring when the block is$5\mathrm{.}40$cm$$from equilibrium.

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

$($c$)$ What is the speed of the block when it is at a position$$xi$/2=2\mathrm{.}70$cm$?$