PULLEYS
Q) A man can apply a maximum effort of 200N. He has to lift a load of 38kgf &
has a single pulley. How should he use it? How much is the effort required if the
pulley is weightless.
MOVABLE PULLEY SYSTEMS
Q) A movable pulley system consists of two movable pulleys. Calculate the distance
moved by the load when effort moves by 60cm. If the minimum effort
required
for the load of 30kgf is 100N then calculate the
i) efficiency
ii) W.O.
iii) W.I
BLOCK & TACKLE SYSTEM
Q) A block & tackle system has 5 pulleys & is 80% efficient. Calculate the MA &
the effort for a 200kgf load.
PROBLEMS FOR PRACTICE
Q1) A block & tackle pulley system has a velocity ratio 3 and efficiency 80%.
Calculate the mechanical advantage of the system & effort required to raise a load
of 300N.
Ans:MA=2.4; E=125N
Q2) A single fixed pulley is used by a boy to lift a load of 400 N through a
vertical height of 5m in 10 seconds. The effort applied by the boy on the other
end of the rope is 480N.
i) What is the velocity ratio of the pulley?
ii) What is the mechanical advantage?
iii) Calculate the efficiency of the machine.
iv) What is the energy gained by the load in 10 seconds?
v) How much power was developed by the boy in raising the load?
Ans:VR=1; MA=0.83; %eff.=83.33%; Energy gained=2000J; P=240W
Q3) A block and tackle system of 5 pulleys is used to raise a load of 50 kgf
steadily through a height of 20 m. The work done against friction is 2000J.
Calculate i) the work done by the effort
ii) mechanical advantage
iii) effort
Ans:Work done by effort=WI=12000J; MA=4.17; E=120N