Question

A truck weighing $1000kgf$ changes its speed from $36km$ $h^{-1}$ to $72km$ $h^{-1}$ in $2$ minutes.$(g=10m{s}^{-2})$. Calculate its power.

• A. $1.25W$
• B. $1.25\times {10}^{6}W$
• C. $1.25\times {10}^{3}W$
• D. $1.25\times {10}^{4}W$

Answer 1

Answer: (C)

$1.25\times {10}^{3}W$

We know that $1km/h=5/18m/s$.
That is $36km/h=10m/s$ and $72km/h=20m/s$.
$K.E=0.5\times m\times v^2$
For work done by the engine we need to take the difference i.e
$W=0.5\times 1000(20\times 20-10\times 10)J$
$W=15\times {10}^{4}J$.
Here $t=2min=2\times 60=120$ seconds.
$P=W/t=15\times {10}^4/120=1250Watt$
Hence power generated is $1250W$ $=1.25\times {10}^{3}W$