Question

A boy lifts a load of 40 kgf through a vertical height of 2m in 5s by using a single fixed pulley when he applies an effort of 48 kgf. Calculate: (i) the mechanical advantage, and (ii) the efficiency of the pulley. Why is the efficiency of the pulley is not 100%? (iii) the energy gained by the load in 5s, and (iv) the power developed by the boy in raising the load.

Answer 1

Given: L = 40kgf,

(ii) If the effort moves a distance d downwards, the load also moves a distance d upwards. So velocity ratio (V.R.) = d/d = 1, 

The efficiency of the pulley is not 100% because some energy is wasted in overcoming the friction in the pulley bearings.