Question

Find the value of friction forces between the blocks $A$ and $B$ and between $B$ and ground (Take $g=10m{s}^{-2}$)

• A. 90 N, 5 N
• B. 5 N, 90 N
• C. 5 N, 75 N
• D. 0 N, 80 N

Answer 1

The correct option is D 0 N, 80 N

Let$,$

$F_1=$ frictional force between $15kg$ block and ground surface

$F_2=$ frictional force between $5kg$ block and $45kg$ block surface

$N_1=$ Normal reaction on block $15kg$ block

]$N_2=$ normal reaction on block $5kg$ block

because there is no upward motion

$N_1=15kg+5kg=20kg$

$N_2=5kg$

F $($limiting$)=$ $\mu N_1=0.6\times 20kg=0.6\times 20\times 10=120N$

because ground can friction force can able to oppose $120N$ if we apply force above $120N$ they only block starts to move$.$ n this block isn't move$.$

$F_1=F$

$F_1=80N$ $($because it is self adjusting force$)$

because there is no actual relative motion and also there is no impending of relative motion $($tendency of relative motion$)$

hence, there no force acting surfaces between $5kg$ block and $15kg$ block

So$$,{F_2} = 0$

Hence,

option $\left(D\right)$ is correct answer.