A car travels at 25m/s for 20 seconds and then decelerates until it stops after a further 10 seconds. Calculate the deceleration of the car, calculate the distance travelled during the 40 seconds

The question does NOT ask how far the vehicle moves when coming to a complete stop, just how far it travels during the period of deceleration.

For the period of deceleration the velocity changes from 25 to 10 m/s so the deceleration is (25–10)/3 = 15/3 = -5 m/s^2

The distance travelled is

s= 1/2 at^2 = 1/2 (5)(3)^2 = 45/2 = 22.5 meters.

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