A $35\mathrm{.}0-$g object connected to a spring with a force constant of $40\mathrm{.}0\frac{N}{m}$ oscillates with an amplitude of $8\mathrm{.}00$ cm on a frictionless, horizontal surface.

$($a$)$ Find the total energy of the system.

The answer has units of milli$-$Joules not Joules. mJ

$($b$)$ Find the speed of the object when its position is $1\mathrm{.}20$ cm $.($Let $0$ cm be the position of equilibrium.$)$

$\frac{m}{s}$

$($c$)$ Find the kinetic energy when its position is $3\mathrm{.}00$ cm $.$

You should be solving this problem without considering the mass of the object. mJ

$($d$)$ Find the potential energy when its position is $3\mathrm{.}00$ cm $.$

$0$

You appear to have correctly calculated the potential energy using your incorrect results from above. mJ