Every surface is rough, and system is at rest choose correct option.

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Friction on m is mg upwards

Friction on 2m by wall is 3mg upwards

Friction on 2m is 2mg upwards

Friction on 2m by m is mg downwards

answer is A, B, D.

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Detailed Solution

a) Friction m is mg upwards

On mass m, the gravitational force acts downwards and due to that friction force acts upwards which is $f_{1} = m g$ and the direction is upward. Hence Option a is correct

b) friction on 2m by wall is 3mg upwards

The friction on 2m by the wall will be equal to the sum of both mg and 2mg gravitational force acting downwards.

$f_{2} = m g + 2 m g = 3 m g$

Hence Option b is correct

c) Friction on 2m is 2mg upwards

It is the same as option 2, so it should be 3mg upward

F = 3mg and the direction is upward

Hence Option c is incorrect

d) Friction on 2m by m is mg downwards

This is similar to option 1 on mass 2m by m is the gravitational force acts downward and due to that friction acts upwards which acts downward on mass 2m.

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