Position and Movement Question 4

咁懶架打佢出來丫麻 >﹏<

a coin and a scrap of paper are released at the same level simultaneously in a vacuum glass cylinder. which of the following statements is not correct?

D: the force acting on the coin is equal to the force acting on the scrap of paper

首先,要知道係地球上面點解coin同埋paper跌既速度唔同, 係因為佢地受到既air resistance問題。

然後要知道, 地球對所有物體既地心加速度都係9.8 ms-2, 所以當係一個真空既程況之下, coin同paper跌既速度會係一樣。

但係呢度講緊既係force, 係呢度係指佢地既weight force, w = mg

我地知道coin 同 paper 既質量唔相等, 但加速度相等都係9.8 (呢條問題入面張紙…應該唔會同個coin同重卦 >﹏<~)

所以地球act on佢地既force係唔相等, 但個加速度就相等。

明白未?

2007-02-26 15:59:49 補充：
OK^^希望你明白呢度,因為係物理入面呢d類似既concept非常重要。佢地既加速度相等唔等於地球對佢地既force就係相等。

To describe the position and movement of every object, you need to know all forces acting on each of the objects.
To allow free fall of objects in vacuum, the only acting force is gravitational force. (i.e. A)
Both objects fall from zero speed at same level, as they have same acceleration, their moving speed are the same at all times (although speed is increasing). therefore B and C are correct.
But this gravitational force (mathematically: F=m*g=m*9.8) is directly proportional to the mass of objects. As we know masses of paper and metal coin are different, thus they experience different magnitude of gravitational force, therefore D is wrong.