Q$2(10$ marks$)$

Block A$,$ with mass $3$ m $,$ slides down an inclined plane S of slope angle $36\mathrm{.}9^($@$)$ at a constant

acceleration of $0\mathrm{.}2$m$//$s$^(2)$ while plank B$,$ with mass m$,$ rests on top of A $.$ The plank is attached

by a cord to the wall $($see Figure $2)$ and note that the coefficient of kinetic friction mu$\_($k$)$ is the

same between A and B and between S and A$.$

$($a$)$ Draw free$-$body diagrams of all the forces acting on blocks A and B separately in the

space below.

$($b$)$ Find the coefficient of friction