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

Acceleration = (final velocity-initial v.) / time

= (0-39) / 9

= - 4.33m/s^2

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