WORK, ENERGY & POWER

WORK, ENERGY & POWER
Key notes:
1. Energy is the capacity to do work. It is measured in joules.
2. The principle of conservation of energy states that energy can neither be
created nor destroyed but it can be changed from one form to another.
3. In a falling object, the potential energy is converted into kinetic energy.
4. When friction is not negligible, work has to be done against it.
5. The main sources of energy are: fossil fuels, hydroelectric schemes, solar
energy, geothermal energy and wind energy.
6. Power is rate of doing work.
7. The unit for power is the watt (W).
Formulas:
 Work done = force x distance moved in the direction of the force
= F x d
= J (joule)
 Kinetic Energy (K.E)
K.E. = 1/2 mv²
m - mass
v - speed
 Gravitational Potential Energy (P.E)
P.E = mgh
m - mass
g - acceleration due to gravity
h - height
 The energy released during a nuclear reaction is given by E = mc².
 Efficiency = (useful energy output/ energy input) x 100%
O LEVEL PHYSICS REVISION NOTES
 POWER
P = E / t
Power = work done / time taken
= energy output / time taken
Unit is the watt (W).