Acar starts from rest and reaches 20 m/s in 5 seconds. the average acceleration of the car is?

4 m/s

Explanation: Acceleration is the rate at which somethings speed changes in a short period of time.  The car's speed started at 0 and went to 20 m/s, which was a change of 20 m/s. It did this in 5 seconds.  So the rate at which the speed changed was 20 m/s / 5 s = 4 m/s

we need to know the time interval during which the force acts. impulse of force = momentum change