Question

A car of mass $1200\, kg$ (together with the driver) is moving with a constant acceleration of $2 \,m / s ^{2}$. How much power does the engine generate at the instance, when the speed reaches $20 \,m / s$ ? (Assume that the coefficient of friction between the car and the road is $0.5$ ).

• A. 48000 W
• B. 120000 W
• C. 168000 W
• D. 288000 W

Answer 1

Answer: (C)

Power of engine overcomes friction and provides necessary acceleration to the car.
Now friction, $f=\mu m g=0.5 \times 1200 \times 10=6000\, N$
and accelerating force, $F=m a=1200 \times 2=2400\, N$
So, total force produced by engine
$=F_{T}=8400\, N$
We know that, the formula of power is
$P=F_{T} v $
Then, $P=8400 \times 20=168000 \,W$