# Power

Question 1 A body does 20 joules of work in 5 sec.what is its power?

Question 2 What is the power of a pump which takes 10 sec to lift 100 kg of water tank situated at a height of 20 m?

Question 3 Define the term power?

Question 4 Give the S.I. unit of power?

Question 5 Define the term watt?

Question 6 How many watts equal one horse power?

Question 7  The power output of an engine is 3 KW.How much work does the engine do in 20s?

Power
Old man takes 10 min to do particular work whereas young man takes 5 min to do same work.
Power is defined as rate of doing work.

work done
Power=——————
Time taken
W
P=—–
t
Power is work done per unit time.
When work is done,an equal amount of energy is consumed.
The S.I. unit of power is Watt(W)
1 watt is the power of an appliance which does work at rate of 1 joules per second.
1 joule
1 Watt=————–
1 Second

1 kilowatt=1000 watt
1KW = 1000 Watt
1 Megawatt=1000000 Watt
Another unit of power is horsepower(h.p.)
1 h.p. =746 watt
1 h.p. = 0.746 KW.
The commercial unit of energy is kilowatt-hour(KWh)
One KWh is the amount of electrical energy consumed when an electrical appliance having a power rating of 1Kw is used for 1 hr.
1 kilowatt-hour =1000 watts for 1 hour.
1 joule
1 Watt=————–
1 second

1kilowatt-hour = 36,00,000 joule

Watt or Kilowatt hour is unit of electrical power.
Kilowatt-hour is unit of electrical energy.
The electrical energy used in homes,shopes,industries is measured in kilowatt-hour(KWh)
1KWh of electrical energy is called as 1 unit of electricity.