Question

A square block of 25 cm side and weighing 20N is hinged at A and rests on rollers at B as shown in fig. It is pulled by a string attached at C and inclined at 300 with the horizontal. Make calculations for the force P to be applied so that the block gets just lifted off the roller.

Answer 1

From the Free body diagram the block is subjected to the following set of forces. 

1. Force P 

2. Weight of the block W 

3. Reaction RA at the hinged point 

4. When the block is at the state of just being lifted off the roller, reaction RB = 0

∑MA = 0

 – P cos 30° × 0.25 – P sin 30° × 0.25 + 20 × 0.125 = 0

– 0.22 P – 0.125 P + 2.5 = 0

P = 7.27N