1) Mechanical efficiency is the measure of the effectiveness of the performance of a mechanical system. T 2) When measuring mechanical efficiency, friction is not taken into account. F 3) If there was no friction on this Earth, cars would not be able travel on roads. T 4) When calculating efficiency, the work output would always be greater than the work input. F 5) Efficiency of a machine can be improved by decreasing friction. T 6) Lubricants are solids and liquids that help decrease friction. T 7) Lubricants can be used to decrease thermal energy given off from light bulbs. F 8) Work output is the total amount of work you apply, including the work input and the friction caused by any moving parts in the machine. F Mechanical Efficiency Problems
1) Tom uses 500 N of force to push a box up a 15 m ramp so that the box 2 m high from the ground. The force of gravity acting on the box is 100 N. What is the efficiency of the ramp?
Work Output = Force x Distance = 500 N x 2 m = 1000 J Work Input = Force x Distance = 100 N x 15 m = 1500 J Mechanical Efficiency = Work Output / Work Input x 100% = 1000 J / 1500 J x 100% = 66.67%
The efficiency of the ramp is 66.67%.
2) An 800 N box is lifted using a second class lever with an input force of 400 N. The load arm is 2 m and the effort arm is 10 m. Calculate the mechanical efficiency of the lever.
Work Output = Force x Distance = 800 N x 2 m = 1600 J Work Input = Force x Distance = 400 N x 10 m = 4000 J Mechanical Efficiency = Work Output / Work Input x 100% = 1600 J / 4000 J x 100% = 40% The mechanical efficiency of the lever is 40%. 3) A machine can do 400 J of work if 500 J of work is put into it. What is the efficiency of this machine?
Mechanical Efficiency = Work Output / Work Input x 100% = 400 / 500 x 100% = 80% The efficiency of this machine is 80%. Short Answer
1) Why is the mechanical efficiency never greater or equal to 100%?
The mechanical efficiency is never greater or equal to 100% because of the frictional force caused by the moving parts of the machine. Also, if the machine did have a mechanical efficiency equal to 100%, then it would have needed to be able to transform energy from one form to another without the loss of energy in the system. If the machine had a mechanical advantage greater than 100%, then it would have needed to somehow generate additional energy which is not possible.
2) Why is a Light Emitting Diode (LED) more efficient than an incandescent light bulb?
A Light Emitting Diode (LED) is more efficient than an incandescent light bulb because it generates a lesser amount of thermal heat caused by friction. A LED converts about 95% of its electricity into light energy, while an incandescent light bulb only converts about 10% of its electricity to light energy.
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Quiz Answers
True and False
1) Mechanical efficiency is the measure of the effectiveness of the performance of a mechanical system. T
2) When measuring mechanical efficiency, friction is not taken into account. F
3) If there was no friction on this Earth, cars would not be able travel on roads. T
4) When calculating efficiency, the work output would always be greater than the work input. F
5) Efficiency of a machine can be improved by decreasing friction. T
6) Lubricants are solids and liquids that help decrease friction. T
7) Lubricants can be used to decrease thermal energy given off from light bulbs. F
8) Work output is the total amount of work you apply, including the work input and the friction caused by any moving parts in the machine. F
Mechanical Efficiency Problems
1) Tom uses 500 N of force to push a box up a 15 m ramp so that the box 2 m high from the ground. The force of gravity acting on the box is 100 N. What is the efficiency of the ramp?
Work Output = Force x Distance
= 500 N x 2 m
= 1000 J
Work Input = Force x Distance
= 100 N x 15 m
= 1500 J
Mechanical Efficiency = Work Output / Work Input x 100%
= 1000 J / 1500 J x 100%
= 66.67%
The efficiency of the ramp is 66.67%.
2) An 800 N box is lifted using a second class lever with an input force of 400 N. The load arm is 2 m and the effort arm is 10 m. Calculate the mechanical efficiency of the lever.
Work Output = Force x Distance
= 800 N x 2 m
= 1600 J
Work Input = Force x Distance
= 400 N x 10 m
= 4000 J
Mechanical Efficiency = Work Output / Work Input x 100%
= 1600 J / 4000 J x 100%
= 40%
The mechanical efficiency of the lever is 40%.
3) A machine can do 400 J of work if 500 J of work is put into it. What is the efficiency of this machine?
Mechanical Efficiency = Work Output / Work Input x 100%
= 400 / 500 x 100%
= 80%
The efficiency of this machine is 80%.
Short Answer
1) Why is the mechanical efficiency never greater or equal to 100%?
The mechanical efficiency is never greater or equal to 100% because of the frictional force caused by the moving parts of the machine. Also, if the machine did have a mechanical efficiency equal to 100%, then it would have needed to be able to transform energy from one form to another without the loss of energy in the system. If the machine had a mechanical advantage greater than 100%, then it would have needed to somehow generate additional energy which is not possible.
2) Why is a Light Emitting Diode (LED) more efficient than an incandescent light bulb?
A Light Emitting Diode (LED) is more efficient than an incandescent light bulb because it generates a lesser amount of thermal heat caused by friction. A LED converts about 95% of its electricity into light energy, while an incandescent light bulb only converts about 10% of its electricity to light energy.