Question

A car running at 54 km/hr is slowed down by 36 km/h in 4 seconds by the application of brakes. Calculate the retardation produced.

• A. 9 km/h${}^2$
• B. 10 km/h${}^2$
• C. 12 km/h${}^2$
• D. 18 km/h${}^2$

Answer 1

The correct option is A 9 km/h${}^2$

Initial velocity (u) = 54 km/hr
Final velocity (v) = (54 - 36) km/hr
Time (t) = 4 seconds
We know v = u - at
$\Rightarrow$ 18 = 54 - a $\times$ 4
or 4a = 54 - 18
or a = $\frac{36}{4}=9km/h^2$
$\therefore$Retardation = 9 km/h${}^2$