Question

A car is running at a speed of 72 km h -1. The driver applies brakes abd the car comes to rest in 10 s. What is the average acceleration

Answer 1

intial speed of car = 72 km/h
= 72×5/18 m/s
= 20 m/s
final speed of car = 0 m/s
time taken for breaking the car = 10 s
use formula,

V = U + at
0 = 20 + a× 10
a = -2 m/s²
hence average acceleration = -2 m/s²

Answer 2

Given,
Initial Speed (u) = 72 km/h or 20 m/s
Final Speed (v) = 0 m/s 
Time taken (t) = 10 s 
Acceleration (a) = ???

We know,
Equation of motion i.e

$\boxed{v = u+at}$

Putting values:
0 = 20 + a × 10
a = -2 m/s²