Find the efficiency of a pulley system which has a mechanical advantage of 2.5 and where the load lifts by 2.5 metres on pulling the rope by 10 m.
- A.62.50%
- B.25.00%
- C.40.00%
- D.100.00%
Correct answer
Explanation
The correct answer is A, 62.50%. The velocity ratio is the distance moved by the effort divided by the distance moved by the load, that is ten divided by two point five, which is four. Efficiency is the mechanical advantage divided by the velocity ratio, so it is two point five divided by four, which is zero point six two five, or sixty-two point five per cent. Option B is wrong because twenty-five per cent would follow from dividing the load distance by the effort distance and treating it as the efficiency. Option C is wrong because forty per cent is the velocity ratio divided by the mechanical advantage, the formula taken upside down. Option D is wrong because an efficiency of a hundred per cent belongs only to an ideal frictionless machine, in which the mechanical advantage would equal the velocity ratio of four.
Read the full article: Simple Machines: Levers, Pulleys, Formulas and PYQs
Practice Questions
View allThe effort applied to move a load is 15 units and the mechanical advantage is observed to be 3. Find the load.
- A.5 units
- B.3 units
- C.15 units
- D.45 units
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Mechanical advantage is defined as the load divided by the effort, so the load is the mechanical advantage multiplied by the effort, that is three multiplied by fifteen, which gives forty-five units.
Read the full explanation →The velocity ratio of a simple machine is the ratio of distance travelled by the ________ to the distance travelled by the ________ in the machine.
- A.load; load
- B.effort; load
- C.load; effort
- D.effort; effort
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Velocity ratio is defined as the distance moved by the effort divided by the distance moved by the load in the same interval of time, and because it depends only on the design of the machine it does not change with friction, unlike the mechanical advantage.
Read the full explanation →Which of the following mechanical devices efficiently distributes or multiplies loads with little effort?
- A.Gears
- B.Lever
- C.Shafts
- D.Bearings
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A lever is a rigid bar turning about a fulcrum, and by the principle of moments the load multiplied by the load arm equals the effort multiplied by the effort arm, so a long effort arm lets a small effort balance a large load; this is the simplest way of…
Read the full explanation →A wheelbarrow is an example of which class of lever?
- A.First class
- B.Second class
- C.Third class
- D.It is not a lever
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In a wheelbarrow the wheel acts as the fulcrum, the load sits in the tray between the wheel and the hands, and the effort is applied at the handles, which is the arrangement of a second class lever; because the effort arm is always longer than the load arm, its…
Read the full explanation →A pair of forceps or sugar tongs is an example of which class of lever?
- A.First class
- B.Second class
- C.Third class
- D.Fourth class
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In a pair of tongs the joint is the fulcrum, the hand presses somewhere in the middle of the arms and the object held lies at the far end, so the effort is between the fulcrum and the load; the effort arm is shorter than the load arm, the mechanical…
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