Question

For the figure shown below, choose the correct option(s) (Assume all surfaces are rough and all velocities are with respect to ground).

• A. Friction force on block E and B is rightward.
• B. Friction force on block E and B is leftward.
• C. Friction force on block A and D is leftwards.
• D. Friction force on block A and D is rightwards.

Answer 1

Answer: (B), (D)

Friction force on block A and D is rightwards.

Kinetic Friction opposes relative slipping. Its acts opposite to the direction of relative velocity.
Velocity of block E w.r.t D,
${\overrightarrow{v}}_{ED}=2\hat{i}-\hat{i}=\hat{i}$
For D, E appears to be moving rightwards, hence friction force on E will be leftwards and on D will be rightwards.
Velocity of block D w.r.t C,
${\overrightarrow{v}}_{DC}=\hat{i}-3\hat{i}=-2\hat{i}$
For C, D appears to be moving lefttwards, hence friction force on D will be rightwards and on C will be lefttwards.
Velocity of B w.r.t A,
${\overrightarrow{v}}_{BA}=5\hat{i}-(-5\hat{i})=10\hat{i}$
For A, B appears to be moving rightwards, hence friction force on B will be leftwards and on A will be rightwards.
Velocity of B w.r.t C,
${\overrightarrow{v}}_{BC}=5\hat{i}-\left(3\hat{i}\right)=2\hat{i}$
For C, B appears to be moving rightwards, hence friction force on B will be leftwards and on A will be rightwards.