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 $20\ ms^{-1}$?

Watt is the SI unit of power. 1 Watt is said to be 1-joule work done per second.

$1 KiloWatt=1000\ Watt$

As given, the mass of the car $m=150\ kg$

Power developed by the engine per kg $=500\ W$

Total power developed by engine $P=150\times500=75000\ W$

Speed of the car $v=20\ ms^{-1}$

Therefore, force exerted by the engine $F=\frac{P}{v}$

$=\frac{75000\ W}{20\ ms^{-1}}$

$=3750\ N$

Therefore, the engine exerts a force of $3750\ N$ in moving the car.

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Updated on: 10-Oct-2022

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