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  4. A car of mass 500 kg is driven with acceleration 1 m / s 2 along straight level road against constant external resistance of 1000 N. When the velocity is 5 m / s the rate at which the engine is working is :

Q. A car of mass $500 \,kg$ is driven with acceleration $1 \,m / s ^{2}$ along straight level road against constant external resistance of $1000\, N$. When the velocity is $5\, m / s$ the rate at which the engine is working is :

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Solution:

For motion of car we use
$F-1000 \,N =500 \times 1$
$F =1500\, N$
Power $P =F \cdot v $
$=1500 \times 5$
$=7500\, W $
$=7.5\, kW$

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