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2007 AL Physics mc Q1
謝謝你，天同知識長。
其實無論我及那怕羞網友心裏都知答案應該是D，但他對我說是否有可能以物理學的學術角度去解釋而不是以常識或體驗去解釋。
例如你首先說的「To establish equilibrium, the direction of forces on rods P and Q shall not be the same. This excludes options B and C」就是他想要的解說方式。
但「Option A is impossible, as rod P would not be in compression.
In option D, just image that if the weight fell down, rod P would be extended and rod Q would be compressed」他認為不是專業的、學術性的解釋，只是常理解釋。他要的不是這個，因為他也能如此解說。
看來他走火入魔妄想騎過愛因斯坦。
知識長，有可能再幫幫他嗎？
謝謝你，知識長，我問他是否己得到他想要的答案，他說OK。
1 個解答
- ?Lv 78 年前最佳解答
The answer is option D
To establish equilibrium, the direction of forces on rods P and Q shall not be the same. This excludes options B and C
Option A is impossible, as rod P would not be in compression.
In option D, just image that if the weight fell down, rod P would be extended and rod Q would be compressed.
2013-03-24 21:57:55 補充：
If the directions of rods P and Q were the same, this would give all left or all right force components. The set up could not be in equilibrium.
2013-03-24 22:23:35 補充：
Next, imagine that if rod Q is not present, then there would be two forces at the hinge, one is the normal reaction givenby the hinge (this acts horizontally to the right), and the other is acting acting vertically upward. Such upward force would be balanced by the weight W.
2013-03-24 22:27:06 補充：
(cont'd)... thus the presence of Q is to provide a left-pointing horizontal force to balance the right-pointing force of Q. A left-pointing force wold mean that Q is in compression.
As there is no numerical figures given in the problem, it cannot be explained by claculations.
2013-03-24 22:28:55 補充：
sorry.. a typing mistake in the last post, it should read:
... thus the presence of Q is to provide a left-pointing horizontal force to balance the right-pointing force of P. A left-pointing force wold mean that Q is in compression.
