一條簡單的物理問題 - Ans.fyi 參考答案

一條簡單的物理問題

Tieria

2010-04-08 3:32 am

1. Two packs of paper R and S are placed one over the other on a table.

http://i617.photobucket.com/albums/tt257/michaelcoco_/9.jpg

A horizontal force F is applied to R. The system is still at rest. Which of the following statements is / are correct?

(1) The frictional force acting on S by R is to the right.
(2) The frictional force acting on S by the table is equal to F.
(3) The system will move if the force F is applied to S.

(1) only.(1) and (2) only(2) and (3) only(1), (2) and (3)
The answer is B.

※試解釋各點對與錯之原因※

回答 (1)

天同

2010-04-08 3:59 am

✔ 最佳答案

Statement (1) is correct.
R tends to slide forward (to the right) relative to S because of the action of F. Hence frictional force acting on R is backward (to the left). The reaction of the frictional force, acting on the top of S, is thus to the right.

Statement (2) is correct.
Following with the explanation given above, S tends to slide forward (to the right), the friction given by the table to S, is thus backward, i.e. to the left.
Since it is given that the system is at rest, all forces balance each other. In other words, all forces equal to F, the applied force.

Statement (3) is wrong.
The reason is apparent. The same force appled to the same system, if originally at rest, will be at rest irrespective of the point of action of the force.

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