力學!!!help,英文答

The student is wrong.

When the cable of the lift breaks, the woman inside undergoes free falling with the lift. The reading of the weighing scale becomes zero because the reaction on the weighing scale by the woman is zero.

By Newton's 3rd law of motion, the reaction acting on the woman by the weighing scale is also zero. So she feels 'weightlessness'

But in fact, this is only her sensation. We people feel our weight because there is a reaction acting on us by the floor.

Now, the woman is free-falling, that means it is falling with the acceleration due to gravity. In her free-body diagram, her weight is the only force acting on her, it is not zero. It is weight = mg.





2009-06-07 20:01:32 補充：
其實我想你明白多啲，所以答咁長。

如果要按marking scheme去答，應該是

2009-06-07 20:01:39 補充：
The student is wrong.

When the cable of the lift breaks, the woman inside undergoes free falling with the lift. The reading of the weighing scale becomes zero because the reaction on the weighing scale by the woman is zero.

2009-06-07 20:01:42 補充：
By Newton's 3rd law of motion, the reaction acting on the woman by the weighing scale is also zero. So she feels 'weightlessness' instead of her weight being zero.