A car is travelling with a speed of $36\ km/h$. The driver applied the brakes and retards the car uniformly. The car is stopped in $5\ sec.$ Find the acceleration of car.

Here given:

Initial velocity $u=36\ km/h$

Final velocity $v=0$                     [Because car stopped]

Time taken to stop the car $t=5\ sec.$

On using equation, $v=u+at$

$0=36+a\times 5$

Or $5a=-36$

Or $a=-\frac{36}{5}=-7.2\ m/s^2$

Here negative $(-ve)$ sign means deceleration.

Thus, the retardation$( Negative\ acceleration)$ of the Car is $7.2\ m/s^2$