Suppose all the surfaces in the previous problem are rough. The direction of friction on B due to A
(a) is upward (b) is downward (c) is zero (d) depends on the masses of A and B.

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1 Answers

(a) is upward

Explanation: 

At equilibrium, the weight of block B (Downward force) has to be balanced by an upward force which is the force of friction applied by block A on B.  

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