A jack$-$in$-$the$-$box toy consists of a clown mounted to a spring inside of a box. When the box open the clown pops out and oscillates. Suppose the clown only oscillates vertically and the clown has a mass of $\mathrm{.}21$ kg$.$ The spring it is mounted on has a force constant of $1\mathrm{.}57$ N$/$m$.$

$($a$)$ What is the maximum velocity of the clown if the amplitude of the oscillation is $4\mathrm{.}00$ cm$?$

$$m$/$s

$($b$)$ How many joules of kinetic energy does the clown have its maximum velocity?