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posted by  cls0411 on 6/5/2008 6:47:22 PM  |  status: Live  

displacement vectors

Course Textbook Chapter Problem
Algebra Based Physics College Physics (7th) by Serway, Faughn, Bennett N/A N/A
Question Details:
You have two displacement vectors: D(arrow above)= (35.0 m, 60.0 degrees north of west) and E (arrow above)= (40.0, west). (a) Find the magnitude and direction of D-E. (b) Find the magnitude and direction of 3D-E.

I have the answers the problem but my own answers are off. ( I got 65 m and 27.8 degrees for part a). What am I doing wrong? Thanks.
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Sage
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posted by SamiLiLOnE on 6/5/2008 7:02:01 PM  |  status: Live
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cls0411's comment:
"Thanks!!"
Response Details:
|DE| = √352 + 402 = 53.15 m

Dx = 35cos60 = 17.5 m          Dy = 35sin60 = 30.3m
Ex = 40cos90 = 0 m               Ey = 40sin90 = 40 m

tanθ = (30.3 + 40)/(17.5 + 0) = 4.02
θ = 76o north of west
 
|3DE| = √(3 x 35)2+ 402 = 98.5 m

3Dx = 3(35)cos60 = 52.5 m         3Dy = 3(35)sin60 = 90.9 m
Ex = 40cos90 = 0                           Ey = 40sin90 = 40 m

tanθ = (90.9 + 40)/(52.5 + 0) = 2.49
θ = 68o     


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