Question

Two identical blocks are kept on rough inclined plane (m = 0.5). The blocks are connected with light string. If mg < F < 2mg, then –

• A. Friction force on block ‘A’ is in upward direction
• B. Friction force on block B may be either in upward direction or downward direction
• C. Friction on block ‘A’ depends upon force ‘F’
• D. Friction force on block ‘B’ may be zero

Answer 1

Answer: (B)

Friction force on block B may be either in upward direction or downward direction

Answer 2

Figure shows forces acting along the string

\ f + $\frac { 3 \mathrm { mg } } { 5 }$ = F – mg

̃ f = F – $\frac { 8 \mathrm { mg } } { 5 }$

\ If F < $\frac { 8 \mathrm { mg } } { 5 }$ ̃ f : – ve ̃ Friction force on block ‘B’ is in upward direction.

F > $\frac { 8 \mathrm { mg } } { 5 }$ ̃ f : + ve ̃ friction force on block ‘B’ is in downward direction.