al physics

用戶40491

2010-06-20 12:17 am

If two velocities each of magnitude v and one of which is directed due north are compounded, which of the following statements concerning the resultant velocity is/are true?

1) It may be zero.
2) It may act due north.
3) It may act due east.

Ans: 1 & 2

Actually I dont understand what is the question asking about...Would you mind to explain the question to me once again and teach me how to do it??

Thank you very much !!! =)

回答 (1)

cipker

2010-06-20 1:54 am

✔ 最佳答案

Consider the diagram,

圖片參考：http://imgcld.yimg.com/8/n/HA00140412/o/701006190086513873424280.jpg

The velocity poiting north is represented by the back arrow.
The other velocity is represented by the red arrow.

The direction of the back arrow is fixed, but the direction of the red arrow is not.

When one rotates the red arrow as shown with centre at O, and resultant velocity (orange arrow) is changed accordingly.

When the red arrow is opposite in direction to the black arrow, they cancel each other and the orange arrow disappears.(It may be zero.)

When the red arrow is in the same direction as the black arrow, the orange arrow points north.( It may act due north.)

But no matter the direction of the red arrow, we can never obtain a orange arrow pointing east or west.

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