A block of mass 4kg is pressed against the wall by a force of 80 N as shown in figure. Determine the value of friction force and block's acceleration $\left(\text{ take }{\mathrm{\mu }}_{\mathrm{s}}=0.2, {\mathrm{\mu }}_{\mathrm{k}}=0.15\right)$

The FBD of the block is as shown in figure.

$\begin{array}{l} \mathrm{N}=80 \cos {37}^{\circ }=64 \mathrm{N}\\ \mathrm{So}, {\mathrm{f}}_{\mathrm{L}}=0.2\times 64=32 \mathrm{N}\end{array}$

As $4\mathrm{g}<80 \sin {37}^{\circ }$, friction force will act downwards. Net applied force in upward direction (excluding friction force) is

           $80\sin {37}^{\circ }-40=48-40=8\mathrm{N}$

As ${\mathrm{F}}_{\text{applied }}$ in vertical direction is less than ${\mathrm{f}}_{\mathrm{L}}$, block will not move in vertical direction and value of static friction force is f = 8 N.