. 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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