Question

A car decreases its speed from $80km{h}^{-1}$ to $60km{h}^{-1}$ in $5seconds$. The acceleration of the car is:

• A. $-1.11m{s}^{-2}$
• B. $-1.52m{s}^{-2}$
• C. $-1.62m{s}^{-2}$
• D. $1.42m{s}^{-2}$

Answer 1

The correct option is A $-1.11m{s}^{-2}$

Given:

Initial velocity:
$u=80km{h}^{-1}$
$u=80\times \frac{5}{18}=22.22m{s}^{-1}$
Final velocity:
$v=60km{h}^{-1}$
$v=60\times \frac{5}{18}=16.67m{s}^{-1}$

Time taken, $t=5s$

Let 'a' be the acceleration of the car.
From definiton of acceleration:
$\therefore a=\frac{v-u}{t}$
$\Rightarrow a=\frac{16.67-22.22}{5}$
$\Rightarrow a=-1.11m{s}^{-2}$
$\therefore$ Acceleration of the car is $-1.11m{s}^{-2}$