Question

If a car at rest is accelerated uniformly to the speed of $144\text{km/h}$ in $20\text{s}$, distance covered by the car in $20\text{s}$ is

• A. $420\text{m}$
• B. $480\text{m}$
• C. $380\text{m}$
• D. $400\text{m}$

Answer 1

The correct option is D $400\text{m}$

Given,
$u=0\text{m/s}$
$v=144\text{km/h}=144\times \frac{5}{18}\text{m/s}=40\text{m/s}$

Now, using eqn. of motion $v=u+at$
$40=0+a\left(20\right)$
or $a=2{\text{m/s}}^2$

Distance covered in $20\text{s}$ is given by
$s=ut+\frac{1}{2}a{t}^2=0\times 20+\frac{1}{2}\times 2\times (20{)}^2$
$s=400\text{m}$