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Question
Draw the diagram of a single movable pulley and obtain its mechanical advantage, velocity ratio, and efficiency.
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Solution
Since it is inconvenient to apply the effort in an upward direction, a single fixed pulley is used to change the direction of effort.
In equilibrium, L = T + T = 2T
E = T
Mechanical advantage =`"Load(L)"/"Effort(E)"=(2"T")/"T"=2`
As the effort is pulled down through a distance dE, the two segments of the thread carrying the movable pulley and the load goes up by dE/2.
Hence, dL = dE/2
Velocity ratio (VR) = `"d"_"E"/"d"_"L"`
= `"d"_"E"/("d"_"E"/2)`
= 2.
Efficiency =`"MA"/"VR"`
= `2/2`
= 1 or 100%.
RELATED QUESTIONS
A pulley system has three pulleys. A load of 120 N is overcome by applying an effort of 50N. Calculate the Mechanical Advantage and Efficiency of this system.
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What is the justification for using the pulley then ?
Define the following term in reference to a gear system of Driving gear ?
What is a single movable pulley? What is its mechanical advantage in the ideal case?
Give reason for the following:
In a single fixed pulley, the velocity ratio is always more than the mechanical advantage.
Give reason for the following:
The efficiency of a pulley is always less than 100%
There is no gain in mechanical advantage in the case of a single fixed pulley. Explain, why the pulley is then used?
A pulley system has a velocity ratio of 4 and an efficiency of 90%. Calculate:
(i) the mechanical advantage of the system.
(ii) the effort required to raise a load of 300 N by the system.
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 |
