Starting from rest, a 5$\mathrm{.}$5 kg block slides 3.2 m down a rough $23\mathrm{.}0$ degree incline in $3\mathrm{.}0$ s$.$ The acceleration of gravity is $9\mathrm{.}81$ m$/$s$^2$ 

a$)$ Find the work done by the force of gravity.

Answer in units of J$.$ 

b$)$ the change in mechanical energy due to friction. Answer in units of J$.$ 

c$)$ the work done by the normal force between the block and the incline. Answer in units of J$.$