Question

A car driver driving at a speed of 90 kmh^-1 applies brakes and brings the car to rest in 20 seconds. The acceleration of the car is

• A. +1 m/s²
• B. -1.5 m/s²
• C. -1.25 m/s²
• D. +2.5 m/s²

Answer 1

The correct option is C

-1.25 m/s²

Given:

Final velocity = 0 m/s

Initial velocity = 90 km/h = $90\times \frac{1000}{3600}m/s=25m/s$. $(1km=1000mand1hr=3600s)$

Time taken = 20 s.

Finding the acceleration:

$$\begin{gathered} Acceleration=\frac{changeinvelocity}{timetaken} \\ =\frac{finalvelocity-initialvelocity}{timetaken} \\ =\frac{0-25}{20}=\frac{-25}{20}=-1.25m/s^2. \end{gathered}$$

Thus, the acceleration of the car is -1.25 m/s².

Hence, option (c) is correct.