A car of mass 1200 kg (together with the driver) is moving with a constant acceleration of 2 m/s. 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).

Power of engine overcomes friction and provides necessary acceleration to the car. Now friction, 

$f=umg=0.5\times 1200\times 10=6000N$
And accelerating force, 
 $F=ma=1200\times 2=2400N$ 
So, total force produced by engine = $F_T=8400N$  We know that, the formula of power is $P=F_{T}v$ then, P = 8400 × 20 = 168000 W.