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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 ms–1?
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Solution
One watt is the power of an agent which does work at the
rate of one joule per second. 1 kilowatt = 1000 watt
= 1000 joule per second (v 1 W = 1 J s−1)
Mass of the car, m = 150 kg
Power developed by engine per kg = 500 W
Total power developed by engine,
P = 500 W x 150
= 75000 W
Speed of car, v = 20 m s−1 Power, P = Fv
=> Force exerted in moving the car, f = `"P"/"v"`
= `(75000"W")/(20 "ms"^-1)`
= 3750 N
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