A race car is moving with a velocity of 144 km/h the driver applies the brakes and the car comes to a halt in 12 seconds what is the average acceleration of the car during those 12 seconds

Average acceleration = (change in speed) / (time for the change)

Change in speed = (speed at the end) - (speed at the beginning)

Change in speed = (zero) - (144 km/hr)

Change in speed = - 144 km/hr

(-144 km/hr) x (1,000 m/km) x (1 hour/3600 sec) = - 40 m/s

Time for the change = 12 seconds

Average acceleration = (-40 m/s) / (12 s)

Average acceleration = - 3.33 m/s² (about 1/3 of a 'G')