Question

Define watt. Express kilowatt in terms of joule per second. A 150 kg car engine develops 500 W for each kg. What force does it exert in moving the car at a speed of 20 m s–1?

Answer 1

Watt is the S.I unit of power.
Definition:
1 watt is the power of an appliance which does the work at the rate of 1 joule per second.
1 watt  =  1 joule/1 second.
1 kilowatt=1000w⇒1000joule/sec
problem:
given:
mass of car = 150kg
power for each kg=500x 150=7500w
speed=20m/s
power=Force x v
∴force=power/v
⇒7500/20⇒3750N

Answer 2

Answer:

1 watt = 1 joule/sec

1 kilowatt = 1000W =1000j/sec

given : mass of car = 150kg

Power exerted for each kg = 500W×150kg=7500W

speed =20m/s

P =F×V

:. F=P/V

F=7500/20= 3750N