Question

A block of mass 4 kg is pressed against the wall by a force of 80 N as shown in Fig. Determine the value of friction force and block's acceleration ( take ${\mu }_s=0.2,{\mu }_k=0.15$)

• A. 8 N, 0 $m{s}^{-2}$
• B. 32 N, 6 $m{s}^{-2}$
• C. 8 N, 6 $m{s}^{-2}$
• D. 32 N, 2 $m{s}^{-2}$

Answer 1

The correct option is A 8 N, 0 $m{s}^{-2}$

From FBD

$N=F\cos 37=80.\frac{4}{5}=64N{f}_{static}={\mu }_{s}N=64\times 0.2=12.8N$

Again

$F\sin 37=80\times \frac{3}{5}=48Nmg=4\times 10=40N$

We find $F\sin 37<mg+f_{m}ax$
Accelerationof block $=0m/s^2$

$\therefore$ friction force$=F\sin 37-mg=8N$ (Downward)