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 ?

Answer 1

Power of an agent is said to be 1 watt if it can ferform 1 joule of work in one second, i.e., 1 W = 1J//s.
Also, 1 k W = 1000 = 1000 J//s
Since power developed for each kg is 500 W, total power developed by the engine of 150 kg car, i.e.,
`P =150 xx 500 W = 7.5 xx 10^4 W`
Speed of the car, `upsilon = 20 m//s`
Since power = force xx speed,
`force = (power)/(speed) = (7.5 xx10^4 W)/(20 m//s) = 3.75 xx10^3 N`