Question

In the figure shown, find the direction of friction on $A$ and $B$ respectively on the surface, which is in contact with the surface of block $A$.

• A. $\text{Forward, Backward}$
• B. $\text{Backward, Backward}$
• C. $\text{Backward, Forward}$
• D. $\text{Forward, Forward}$

Answer 1

The correct option is C $\text{Backward, Forward}$

Velocity of block A w.r.t B,
$v_{AB}=4\hat{i}-2\hat{i}=2\hat{i}m/s$
That is for $B$, $A$ appears to move forwards.
Hence, for block $A$, friction will act backwards and for $B$ in forward direction. (Since friction opposes relative motion)
Thus, the FBD can be shown as