Question

A car moving along a straight line at a speed of $72\mathrm{km}{\mathrm{h}}^{-1}$ stops in $5\mathrm{s}$ after the brakes are applied Find the acceleration

Answer 1

Step 1: Given Data

1. A car moves in a straight-line path.
2. The speed of the car is$72km/h$. Converting the value in$m/s$ we get$72\times \frac{5}{18}=20m/s$
3. At last, the car stops. So the final speed$\left(v\right)$ of the car is zero.
4. The car moves for a time of$5s.$

Step 2: Calculating the acceleration of the car

Here$u=20m/s,v=o,t=5s$

by applying the first equation of motion, we get$v=u+at$

$\Rightarrow 0=20+a\times 5$

$\Rightarrow 5a=-20$

$\Rightarrow a=\frac{-20}{5}=-4m/s^2$

here the negative sign shows that after applying the brakes, the car starts to decelerate and finally comes to rest.

Hence, the acceleration of the car is$-4m/s^2$