All surfaces are rough . Draw the friction force on A & B

Explanation

Kinetic friction acts to reduce relative motion.
Summary
We can summarise the laws of friction between two bodies in contact as follows `:`
(i) If the bodies slip over each other, the force of friction is given by
`f_(k ) = mu_(k) N `
where N is the normal contact force and `mu_(k)` is the coefficient of kinetic friction between the surfaces.
(ii) The direction of kinetic friction on a body is opposite to the velocity of this body with respect to the body applying the force of friction.
(iii)If the bodies do not slip over each other, the force of friction is given by
`f _(s) le mu_(s) N`
where` mu_(s)` is the coefficient of static friction between the bodies and N is the normal force between them.The direction and magnitude of static friction are such that the condition of no slipping between the bodies is ensured.
(iv) The frictional force `f_(k) ` or `f_(s)` does not depend on the area of contact as long as the normal forc N is same.