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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
State two functions of a machine.
Draw a neat labelled diagram showing a pulley being used to lift a load. How are load and effort related in an ideal situation?
Define the following term in reference to a gear system for Gear ratio ?
Define the following term in reference to a gear system for Gain in torque ?
In which direction does the force need to applied, when a single pulley is used with a mechanical advantage greater than one? How can you change the direction of force applied without altering its mechanical advantage? Draw a labelled diagram of the system.
Differentiate between a single fixed pulley and a single movable pulley.
What is the use of a fixed pulley?
Give reason for the following:
In case of a block and tackle system, the mechanical advantage increases with the increase in the number of pulleys.
Draw the diagram of a single movable pulley and obtain its mechanical advantage, velocity ratio, and efficiency.
Complete the table.
| S. No | Types of Simple Machine | Example |
| 1. | Pulley | |
| 2. | Wheel and axle | |
| 3. | Wedge | |
| 4. | Inclined plan | |
| 5. | Lever | |
| 6. | Screw |
