Physics Exam1

答案是C
因為動能+勢能是一個不變的數值
現在個支箭在同一位置
即是勢能一樣
推測到動能一樣
亦即速率一樣


2007-01-05 15:01:26 補充：
其實我都唔知閣下prefer中文抑或英文﹐不過我自己用中文答好過用英文答﹐所以0米用中文。反正MC又唔需要用中文﹐最緊要明白點做

2007-01-05 15:01:58 補充：
反正MC又唔需要用英文

Since in the question, it is stated that the arrow returns to the same height.

Therefore, there is neither gain nor loss of gravitational potential energy (g.p.e.) for the arrow.

Assuming that air resistance is negligible, there is no kinetic energy (k.e.) loss for the arrow.

Hence, at the moment when the arrow returns to the same height, the mechanical energy is conserved and the kinetic energy of the arrow remains the same as the moment when it was shot.

Thus, its speed will be vO again.

Answer: C

Note: Since in the question choices, the word used is "speed" but not "velocity". Therefore we can choose C even though the directions of movement at that two points are different.