WEEK 10
SUBJECT: BASIC SCIENCE
CLASS: GRADE 8
TERM: SECOND
TOPIC: WORK, ENERGY AND POWER
(CONTINUED)
POWER: Power is defined
as the time rate of doing work. Like work, power is a scalar quantity. That is
a quantity which has magnitude but no direction. Some units often used for the
measurement of power are the watt (W) (1
Joule of work per second) and the horse power (550 foot-pounds of work
per second). A small engine can do as much work as a larger engine, but it
takes longer time to do it. The larger engine can do work at a faster rate.
Hence, the rate at which work is done is called the power.
Formula for
Power=Work done/Time taken or Energy transferred/ Time taken
1Kilowatt (kW)=
103
1Megawatt (MW)
=106
Calculation: A motor pump
lifts 50Kg of water to a height of 10m in 10 second. Calculate the power of
motor pump. (Take g=10ms-2)
Solution: Mass of water =
50Kg
Height = 10M
Time taken=1s
Work
done = m*g*h= 50*10*10
Now, power =
Work done/time taken =5000/10 = 500W
ENERGY TRANSFER
WHEN WORK IS DONE
According
to the law of conservation of energy, the sum total of energy in a system is a
constant quantity. It can neither be created nor destroyed. However, energy can
change from one form to another. The transformation of energy from one form to another
results in work done.
For
example
·
For
pulling or pushing a load, we are applying chemical energy obtained from food.
This chemical energy gets converted into kinetic energy of the load.
·
When
you rub your palms against each other, kinetic energy of your palms get
converted into heat energy.
·
When
you switch an electric bulb, electrical energy gets converted into light
energy.
·
All
modern automobiles need heat energy. Whether it is a heavy truck or diesel
railway engine, all use heat energy of burning petrol or diesel for doing work.
ASSIGNMENT
1.
What is power? State the formula and unit.
2.
State the law of conservation of energy.
3.
Describe energy transformation with two examples.
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