Question

A car traveling at 39 m/s starts to decelerate steadily. It comes to a complete stop in 9 seconds. What is its acceleration?

Answer 1

Acceleration = (change in speed) / (time for the change)

Change in speed = (end speed) - (start speed) = (zero - 39 m/s) = -39 m/s

time for the change = 9 seconds

Acceleration = (-39 m/s) / (9 seconds)

Acceleration = -4.33 m/s²

Answer 2

acceleration= (final velocity-initial v.)/time
= (0-39)/9
= -4.33m/s^2