It takes 5 seconds for the car to stop from braking. During this period, the distance of the car before 1 second is 9 m, 7 m, 5 m, 3 m and 1 m respectively Ask: the average speed of the car in the first 1s, the first 2S, the first 3S, the first 4S and the whole journey. Which of the five average speeds is closest to the instantaneous speed when the car closes the throttle? Is it slightly larger or smaller than this instantaneous speed? We must answer it!

It takes 5 seconds for the car to stop from braking. During this period, the distance of the car before 1 second is 9 m, 7 m, 5 m, 3 m and 1 m respectively Ask: the average speed of the car in the first 1s, the first 2S, the first 3S, the first 4S and the whole journey. Which of the five average speeds is closest to the instantaneous speed when the car closes the throttle? Is it slightly larger or smaller than this instantaneous speed? We must answer it!

Because of the shift from the last one second
at^2/2=1
a/2=1
a=2
Average velocity in the first 1s = 9 / 1 = 9m / S
Average speed in the first two seconds = (9 + 7) / 2 = 8m / S
Average velocity in the first 3 s = (9 + 7 + 5) / 3 = 7m / S
Average speed in the first 4S = (9 + 7 + 5 + 3) / 4 = 6m / S
Average speed of the whole journey = (9 + 7 + 5 + 3 + 1) / 5 = 5m / S
Instantaneous speed when closing throttle = at = 5 * 2 = 10m / S
Therefore, the average speed in the first second is closest to the instantaneous speed when the throttle is turned off, but slightly smaller than the instantaneous speed