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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
Prepared By Mr.Leon from JJ Super Education.
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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
Work
1. Work done by a constant force is given by the product of the force and the distance moved
in (parallel) the direction of the force.
2. The unit of Nm(Newton metre) or J(Joule).
3. Work is a scalar quantity.
4. Formula
Prepared By Mr.Leon from JJ Super Education.
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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
When the direction of force and motion are same, θ = 0o, therefore cosθ = 1
Work done,W=Fs
Example:
A force of 50 N acts on the block at the angle shown in
the diagram. The block moves a horizontal distance of
3.0 m. Calculate the work being done by the force.
Example:
Diagram above shows a 10N force is pulling a metal. The friction between the block and the floor is 5N. If the distance travelled by the metal block is 2m, find
1. the work done by the pulling force
2. the work done by the frictional force
Energy
1. Energy is defined as the capacity to do work.
2. Work is done when energy is converted from one form to another. 3. The unit of work is Nm or Joule(J)
Prepared By Mr.Leon from JJ Super Education.
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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
Gravitational Potential Energy
Gravitational potential energy is the
energy stored in an object as the result
of its vertical position (i.e., height).
Elastic Potential EnergyElastic potential energy is the energy stored in elastic materials as the result of their stretching or compressing.
Equation of Kinetic Energy
Is the energy that a body in motion.
Example
Determine the kinetic energy of a 2000-kg bus that is moving with a speed of 35.0 m/s.
Power
Power is the rate at which work is done, which means
how fast a work is done.
Prepared By Mr.Leon from JJ Super Education.
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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
Prepared By Mr.Leon from JJ Super Education.
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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
1) Ep=Ek (Potential Energy = Kinetic Energy)
2) Energy cannot be created or destroyed. It can be transformed from one to form to another, but the total kinetic energy in a system is constant.
Prepared By Mr.Leon from JJ Super Education.
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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
Prepared By Mr.Leon from JJ Super Education.
8
2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
Prepared By Mr.Leon from JJ Super Education.
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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
Prepared By Mr.Leon from JJ Super Education.
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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
Air Conditioner
1. Switch off the air conditioner when not in use.
2. Buy the air conditioner with suitable capacity according to the room size.
3. Close all the doors and windows of the room to avoid the cool air in the room from flowing out.Refrigerator
1. Always remember to close the door of refrigerator.
2. Open the refrigerator only when necessarily.
3. Always keep the cooling coil clean.
Prepared By Mr.Leon from JJ Super Education.
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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
4. Defrost the refrigerator regularly.
5. Choose the refrigerator with capacity suitable for the family size.
6. Refrigerator of large capacity is more efficient compare with refirgerator of small capacity.Lamp or Light Bulb
1. Use fluorecent bulb rather than incandescent bulb. Fluorescent bulbs are much more efficient than
incandescent bulbs.
2. Use a lamp with reflector so that more light is directed towards thr desirable place.Washing Machine
1. Use front-loading washing machine rather than top-loading wahing machine because it uses less water
and electricity.
Prepared By Mr.Leon from JJ Super Education.
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2.10 Work, Power, Energy, Efficiency2.11 Power Efficiency 100%
2. Use washing machine only when you have sufficient clothes to be washed. Try to avoid washing small
amount of clothes.
Prepared By Mr.Leon from JJ Super Education.
