Question

The power of engine of a car of mass 1200 kg is 25 kW.The minimum time required to reach a velocity of 90 Km/h by the car after starting from rest is

Answer 1

Given,

$m=1200kg$

$P=25kW$

$v=90km/h=\frac{90\times 1000}{60\times 60}=25m/s$

$u=0m/s$

From work energy theorem,

$W=\Delta K$

$W=\frac{1}{2}m(v^2-u^2)$

$W=\frac{1}{2}\times 1200(25\times 25-0^2)$

$W=375kJ$

Power, $P=\frac{W}{t}$

$t=\frac{W}{P}=\frac{375kJ}{25kW}$

$t=15sec$

The minimum time required is $15sec$.