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?

Soln:

Power of an object which does work at 1 Joules/sec is called watt

1 watt= ^{𝑱𝒐𝒖𝒍𝒆}

𝒔𝒆𝒄𝒐𝒏𝒅

1 kilowatt= 1000watts=1000J/sec mass of car = 150kg

power for each kg=500x 150=7500w

speed=20m/s power=Force x v

∴force=power/v 7500

20

=3750N