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प्रश्न
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.
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उत्तर
Given:
L = 40 kgf,
dL = 2m,
t = 5 s,
E = 48 Kgf.
(i) Mechanical advantage (M.A.) =`"L"/"E"=40/48=5/6=0.833`
(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,
Efficiency = `"M.A."/"V.R."=0.833/1`
= 0.833 (or 83.3%).
The efficiency of the pulley is not 100% because some energy is wasted in overcoming the friction in the pulley bearings.
(iii) The energy gained by the load in 5s = Load × Displacement of load in 5s
= 40 kgf × 2m
= 80 kgf × m.
(iv) Power developed by the boy =`"Effort×Displacement of effort"/"Time"=(48"kgf"×2"m")/(5"s")`
= 19.2 kgf × ms−1.
संबंधित प्रश्न
A pulley system with VR = 4 is used to lift a load of 175 kgf through a vertical height of 15 m. The effort required is 50 kgf in the downward direction. (g = 10 N kg-1)
Calculate:
- Distance moved by the effort
- Work done by the effort
- M.A. of the pulley system
- Efficiency of the pulley system
From the diagram given below. answer the question that follows:
1) What kind of pulleys are A and B?
2) State the purpose of pulley B.
3) What effort has to be applied at C just raise the load L = 20 kgf?
(Neglect the weight of pulley A and friction)
Select the correct alternative:
A pulley is used because of it
What is a pulley?
Define the following term in reference to a gear system for Gear ratio ?
What should be the gear ration of a car : equal to 1, less than 1 or greater than 1, while gaining speed on the road ?
Give two reasons why the efficiency of a single movable pulley system is not 100%.
The diagram below shows a pulley arrangement.
- Name the pulleys A and B.
- In the diagram, mark the direction of tension on each strand of string.
- What is the purpose of the pulley B?
- If the tension is T, deduce the relation between
- T and E, and
- E and L.
- What is the velocity ratio of the arrangement?
- Assuming that the efficiency of the system is 100%, what is the mechanical advantage?
State two reasons, why the efficiency of a pulley system is not 100 percent?
A type of single pulley is very often used as a machine even though it does not give any gain in mechanical advantage. Name the type of pulley used.
