Question

Figure shows the combination of two pulleys P₁ and P₂ used to lift up a load W. 

1. State the kind of pulleys P₁ and P₂.
2. State the function of the pulley Р₂.
3. If the free end F of the string moves through a distance y, by what distance is the load W raised?
4. What effort E has to be applied at C to just raise the load W = 30 kgf? Neglect both the weight of the pulley P1 and the friction.

Answer 1

(a) P₁​ is a single movable pulley, as it moves upward with the load W. P₂​ is a single fixed pulley, as it remains fixed to the support.

(b) The function of P₂​ is to change the direction of the effort. It allows the effort to be applied downwards at the free end F.

(c) In this system, the velocity ratio is 2. Therefore, if the free end moves through a distance y, the load rises through:

Distance moved by load = `"distance moved by effort"/2`

= `y/2`

(d) The load is supported by two segments of the string, each having tension T:

W = 2T

30 = 2T

T = 15 kgf

Since E = TE, the effort required is:

E = 15 kgf