Physics - Ans.fyi 參考答案

Physics

2012-06-17 7:39 pm

First question:
Three girls A, B and C run at steady speeds from point X to point Y along different paths as shown. They take the same amount of time to complete the journey.

圖片參考：http://imgcld.yimg.com/8/n/HA01132001/o/701206170015513873410980.jpg

Is the following statement correct?
Girl A has the highest speed.

Second question:
Is the following statement correct?
An object moving at a constant speed must have zero acceleration.

Third question:
Force F is the resultant force of a 2N force and a 5N force. Which of the following is the possible magnitude of F?
(1) 2N
(2) 3N
(3) 5N

更新1:

I still don't quite understand the second question~>

回答 (1)

天同

2012-06-17 8:04 pm

✔ 最佳答案

1. The statement is correct.
Girl A travels the longest distance in the same time as other girls do.

2. No.
An moving object changes its direction at constant speed is subjected to an acceleration.

3. (2) and (3) are possible.
F must be between (5+2) N = 7 N and (5-2) N = 3 N

2012-06-17 16:02:40 補充：
Acceleration is the rate of change of velocity. But velocity has both magnitude and direction. When there is a change in the direction of velocity, but no change in magnitude (i.e. no change in speed), there is a velocity change. That is, there is an acceleration.

2012-06-17 16:03:13 補充：
An example is an object performing a circular motion.

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