Question

The figure shows the combination of a movable pulley P₁ with a fixed pulley P₂ used for lifting up a load W. 

(a) State the function of the fixed pulley P₂ 

(b) If the free end of the string moves through a distance x, find the distance by which the load W is raised. 

(c) Calculate the force to be applied at C to just raise the load W = 20kgf, neglecting the weight of the pulley P₁ and friction.

Answer 1

(a) The fixed pulley P₂ only changes the direction of the force i.e. force can be applied downwards which is more convenient. 

(b) The load will be raised by a distance x/2. 

(c) Distance moved by load dL = x/2 

Distance moved by the effort dE = x 

Load (L) = 20 kgf 

Effort = ? 

Load × Load arm = effort × effort arm

20 x x/2 = x x E or E = 10kgf.