速度-位移-加速度

Be aware that the velocities in your given diagram is the final velocity at each time interval. For example, v = 2m/s is the final velocity right at 1 s, and v = 4 m/s is the final velocity at 2 s and so on.

You cannot use the final velocity to calculate the displacement covered in the previous second. This would clearly over-estimate the result. For example, from t= 0s to t = 1s, the final velocity v = 2 m/s doesn't imply that the displacement is this time interval is 2 m.

To find the displacement, you need to use the average velocity during each time interval. Thus, the average velocity from t=1s to t=2s is (0+2)/2 m/s = 1 m/s. The displacement is 1 x 1 (velocity x time) = 1 m.

Likewise, the average velocity from t=2s to t=3s is (2+4)/2 m/s = 3 m/sHence, displacement = 3 x 1 m = 3 m.The average velocity from t=3s to t=4s is (4+6)/2 m/s = 5 m/s
Hence, displacement = 5 x 1 m = 5 m
Therefore, total displacement from t=0s to t=3s is (1+3+5) m = 9 m
The same value as that using the equation of motion: s = ut + (1/2).at^2

你可以問下老師。有冇错。

加速度為2ms^-2，不代表（例如）t=1 到t=2 之間的時間，速度都是固定的2m/s；實際上在這一秒時間之內，速度仍不斷上升。
你用「數」的方法，是假定了在t=1 到t=2 之間的時間，速度是固定的，答案當然不對。

你可以問下老師漏！你一o