Calculations for force:
A square block having 25cm side and weighing 20N is hinged at point A and rests on rollers at point B as shown in the figure given below. It is pulled by string attached at point C and inclined at 300 with horizontal. Make calculations for force P to be applied so that block gets lifted off the roller only.
Sol.: From Free body diagram the block is subjected to following set of forces.
1. Force P
2. Weight of block W
3. Reaction RA at hinged point
4. When block is at the state of being lifted off the roller only, reaction RB = 0
∑MA = 0
- Pcos30° × 0.25 - Psin30° × 0.25 + 20 × 0.125 = 0
- 0.22 P - 0.125P + 2.5 = 0
P = 7.27N .......ANS