Question

A car decreases its speed from 80 kmph to 60 kmph in 5 seconds, the magnitude of deceleration of the car is

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

Answer 1

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

Given, initial velocity, $u=80kmph=80\times \frac{5}{18}=22.22m{s}^{-1}$

final velocity, $v=60kmph=60\times \frac{5}{18}=16.67m{s}^{-1}$

and time taken, t = 5 s

Let 'a' be the acceleration of the car.
We know from first equation of motion, $v=u+at$
$\therefore a=\frac{v-u}{t}$
$\Rightarrow a=\frac{16.67-22.22}{5}$
$\Rightarrow a=-1.11m{s}^{-2}$
$\therefore$ Acceleration of the car is $-1.11m{s}^{-2}$

Note: Negative sign show that the car is decelerating.