A truck starts from rest and rolls down a hill with a constant acceleration.

Solution:

Initial velocity of truck, $\mathrm{u}=0 ;$ time, $\mathrm{t}=20 \mathrm{~s} ;$ distance covered, $\mathrm{s}=400 \mathrm{~m} ;$ acceleration,
$\mathrm{a}=? ;$ mass of truck, $\mathrm{m}=7$ metric tonnes $=7000 \mathrm{~kg} ;$ force on truck, $\mathrm{F}=?$

We know, $\mathrm{s}=\mathrm{ut}+\frac{1}{2} \mathrm{at}^{2}$

$\Rightarrow 400=0 \times 20+\frac{1}{2} \times \mathrm{a} \times(20)^{2}$

$\Rightarrow 400=200$ a or $a=\frac{400}{200}=2 \mathrm{~ms}^{-2}$

Force on truck, $\mathrm{F}=\mathrm{ma}=7000 \times 2=14000 \mathrm{~N}$