Question

A car is moving in a straight line with speed $18km$ $h^{-1}$. It is stopped in $5s$ by applying the brakes. Find : (i) the speed of car in $m{s}^{-1}$. (ii) the retardation and (iii) the speed of car after $2s$ of applying the brakes.

• A. $5m{s}^{-1}$
• B. $1m{s}^{-1}$
• C. $3m{s}^{-1}$
• D. none on these

Answer 1

The correct option is A $5m{s}^{-1}$

Given, $Speed=18km/h,t=5s$

a)The speed of the car in $m/s$=$18\times \frac{5}{18}=5m/s$

b) The retardation is:

$a=\frac{v-u}{t}=\frac{0-5}{5}=1m/s^2$

c) The velocity of the as a funcition of time $2s$is:

$v\left(t\right)=5-t\Rightarrow v\left(t\right)=5-2=3m/s=10.8km/h$