Advertisements
Advertisements
Question
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
Advertisements
Solution
1) Displacement due to the effort is VR = 4
Load (L) = 175 kgf
Effort (E) = 50 kgf
Load displacement (dL) = 15 m
`VR = d_E/d_L`
Effort displacement (dE) = 4 × dL
= 4 × 15
= 60 m
Distance moved by the effort is 60 m
2) Work done by the effort is calculated using the following formula.
Work done by effort (WE) = `"Force"_"Effort" xx d_E`
WE = 50 × 60
= 3000 J
3) Mechanical advantage of the pulley system is calculated as
MA of the pulley system = `"Load (L)"/"Effort (E)"`
= `175/50`
= 3.5
4) Efficiency of the pulley is the ratio of work output to the work input required by the system
Efficiency of the pulley system (η) = `"Work output (Work Done by Load)"/"Work input (Work Done by Effort)"`
Work done by load = ForceLoad x dL
= 175 × 15
= 2625 kgf
:. η = `2625/3000`
= 0.875 × 100
= 87.5 %
APPEARS IN
RELATED QUESTIONS
A boy uses a single fixed pulley to lift a load of 50 kgf to some height. Another boy uses a single movable pulley to lift the same load to the same height. Compare the effort applied by them. Give a reason to support your answer.
Select the correct alternative:
A pulley is used because of it
What is a pulley?
Draw a neat labelled diagram showing a pulley being used to lift a load. How are load and effort related in an ideal situation?
Solve the following numerical problem.
What effort will be required to lift a load of 500 N by a single movable pulley? [Hint: Mechanical advantage of a single movable pulley is two].
Name a machine to change the direction of force ?
The diagram below shows an arrangement of three pulleys A, B, and C. The load is marked as L and the effort as E.
- Name the Pulleys A, B, and C.
- Mark in the diagram the directions of load (L), effort (E) and tension T1 and T2 in the two strings.
- How are the magnitudes of L and E related to the tension T1?
- Calculate the mechanical advantage and velocity ratio of the arrangement.
- What assumptions have you made in parts (c) and (d)?
What is a block and tackle system of pulleys?
What is a block and tackle system of pulleys? What precautions would you observe while rounding the string so that the effort is applied in the downward direction?
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 |
