Applied math~ Vectors~~

👨🏻‍🏫 學術台數學

[匿名]

2009-09-17 3:11 am

please look at this picture:

http://ser1.share.ysk.cc/upload/photo/20090916/1253100024-HKTVXfhim2.png

How to do part (a)??

answer is sqrt{3}

thx..

更新1:

Sorry, the answer is : sqrt{3} P

回答 (1)

Prof. Physics

2009-09-17 3:27 am

✔ 最佳答案

a. Let @ be the angle between OA and OB

By cosine rule,

P2 = P2 + Q2 - 2P X Qcos@ (resultant of forces)

Q = 0 (rejected) or 2Pcos@ ... (1)

Once again, by cosine rule,

P2 = (2P)2 + Q2 - 2(2P)Qcos@

-3P2 = 4P2cos2@ - 8P2cos2@

cos2@ = 3/4

cos@ = sqrt3 / 2 (taking the positive root)

Therefore, By (1), Q = 2Pcos@ = Psqrt3

參考: Physics king

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