Question

2. A fixed pulley is driven by a 100 kg mass falling at
a rate of 8.0 m in 4.0 s. It lifts a load of 75.0 kgf.
Calculate :
(a) the power input to the pulley taking the force of
gravity on 1 kg as 10 N.
(b) the efficiency of the pulley, and
(c) the height to which the load is raised in 4.0 s.
no II​

Answer 1

Explanation:

Load = 500 kgf

Mass of falling object = 100 kg

Displacement of effort = 8.0 m

Time taken = 4.0s

(a) Effort = 100 X 10 = 1000 kgf

Power Input = displacement x effort/time = 8 x 1000/4 = 2000W

(b) The efficiency of the pulley is = 75% = 0.75

Mechanical advantage of this system M.A = Load/Effort = 500/100 = 5

Velocity ratio of this system V.R = M.A/η = 5/0.75 = 20/3

Displacement of load D= displacement of effort/V.R = 3 x 8/20 = 1.2