Question

A truck weighing 1000 kgf changes its speed from 36 km $h^{-1}$ to 72 km $h^{-1}$ in 2 minutes.Calculate:

(i) the work done by the engine,and

(ii) its power.(g=10 m$s^{-2}$)

Answer 1

(i)

Step 1, Given data

Mass of the truck = 1000 kg

Initial velocity, $u=36kmph=36\times \frac{5}{18}m/s=10m/s$

Final velocity, $v=72kmph=20m/s$

Step 2, Finding the work done

We know,

Work done = Change in kinetic energy

So, $Workdone=\frac{1}{2}m(v^2-u^2)$

Putting all the values

$Workdone=\frac{1}{2}\times 1000({20}^2-{10}^2)$

After solving

$Workdone=150000J$

Hence the work done by the engine is 150000 J

(ii)

We know,

Power $=\frac{Workdone}{Time}=\frac{1.5\times {10}^5}{120}=1250W$