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- 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
. 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
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.
Best Answer
(a) Effort driving the pulley is,
E = mg
= 100 × 10
= 1000 N
Input power is,
Pin = 2000 W
(b) Load pulley by the pulley is,
L = 75 × 10
= 750 N
Hence, M.A is,
M.A = L / E
= 750 / 1000
= 0.75
When the effort moves by a distance d downwards, the load moves by the same distance upwards. Thus,
V.R = 1
Therefore efficiency is,
η = M.A. / V.R.
= 0.75 / 1
= 0.75
= 75%
(c) The load moves by the same distance upwards when the effort moves by a distance d downwards. So, height to which the load moves is 8 m
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