## 2007-09-19

### Nota Fizik: WORK

Here is the simplification of explanation for Work, Energy, Power and Efficiency

Work, Energy, Power and Efficiency

Work
1. Work is defined as the product of the applied force and the displacement of an object in the direction of the applied force.
2. W = F x S
3. W= work done, F = force applied, S = displacement in the direction of force.
4. SI unit for work = Joule (J), other unit = Nm

5. Work is not done when:
a. The object is stationary aka not moving
b. No force is applied on the object in the direction of displacement.
c. The direction of motion of the object is perpendicular to that of the applied force.
6. When work is done to an object, energy is transferred to the object.

Energy (Energy is the capacity to do work)
1. Energy exists in different forms: kinetic energy, gravitational potential energy, elastic potential energy, sound energy, heat energy, light energy, electrical energy and chemical energy.
2. The unit for energy is Joule (J) – same as work
3. The work done is equal to the amount of energy transferred.
4. Kinetic energy is the energy of an object due to its motion.
5. Kinetic energy or work done is given by:
a. ½ Mv2

b. M = mass, v = velocity
c. Unit: Joule /
-->
kgm2s-2

6. Gravitational potential energy is the energy of an object due to its higher position in the gravitational field.
a. E = mgh
b. M = mass, g = acceleration due to gravity, h = height in metre

Conservation of energy
1. The principle of conservation of energy states that energy cannot be created or destroyed but can change from one form to another form of energy.
2. Total amount of energy remains the same.
3. When water falls from a dam, its potential energy changes to kinetic energy.
4. When a swing moves from one position to another position, its potential energy changes to kinetic energy alternately.

Power
1. Power is defined as the rate of doing work.

a. Power = (Work / Time)

b. P = power, W = work, T = time

2. SI unit for work is = watt (W).

Efficiency

1. Efficiency of a device is defined as the percentage of the energy input that is transformed into useful energy.

2. Efficiency = (useful Energy output / Energy input ) X 100%

a. Efficiency = (Useful power output / Power input) X 100%

b. Unit is given in percentage.

You must know the importance of maximising the efficiency of device.

#### 18 comments: Anonymous said...

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Good post. It'll be better if there are some questions. Anonymous said...

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Very brief, please consult more on KCSE syllabus. Good job anyway!Thank you. Anonymous said...

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Twin said...

Thank you so much, i can understand clearly the sub. Thank u, Anonymous said...

it is help but it would be better if you make a list of formula. Daniel Vine said...

i think Physics would have been much easier if the tree fell on Newton's head instead of the apple Anonymous said...

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That helped me a lot. Some practice questions could make it even more effective. Otherwise, keep the fire blazing !!! Anonymous said...

These notes are awesome because they don't have the nonsense you don't need to understand the concept.

DAVID MWENDA said...

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