Given in the figure are two blocks of A and B of weight $20 N$ and $100 N,$ respectively. These are being pressed against a wall by a force $F$ as shown. If the coefficient of friction between the blocks is $0.1$ and between block B and the wall is $0.15,$ the frictional force applied by the wall on block B is:

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$120 N$

$150 N$

$100 N$

$80 N$

answer is A.

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Detailed Solution

As the both the masses are in equilibrium the static friction will be acting on blocks which can be found from balancing the forces in vertical direction.
The FBD of block A
Writing force balance in vertical direction for block A, $f_{1}$ = weight of the block A =20 N

Writing force balance in vertical direction for block B

$f_{1} - f_{2}$ = weight of the block B 100 N

The value of frictional force between wall and block B is 120 N

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