Question

Block A mass 2 kg is placed over a block $B$ mass 8 kg. The
combination is placed on a rough horizontal surface. If $g=10m{s}^{-2}$,
coefficient offiiction between $B$ and floor $=0.5$, coefficient offfiction
betweenA and $B=0.4$ and a horizontal force on 10 $N$ is placed of8 kg
block, then the force friction between A and $B$ is:

• A. 100N
• B. 50N
• C. 40N
• D. None of these

Answer 1

The correct option is C 40N

$f_1+f_2=10N$

$f_1=$friction b/w floor and B

$f_2=$ friction b/w B and A

$m_1=8kg;m_2=2kg$

$(\mu {)}_1=0.5(\mu {)}_2=0.4$

$f_1=R\left({\mu }_1\right)f_1=(m_1+m_2)g\left({\mu }_1\right)$

$f_1=(2+8)\times 10\times 0.5$

$f_1=50N$

and $f_1+f_2=10N\Rightarrow f_2=-40N$ (-ve due to opposition)