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Need Vector Help

  1. Jan 30, 2005 #1
    Hey guys, I need your help figuring out what I am doing wrong.

    Two beetles run across flat sand, starting at the same point. Beetle 1 runs 0.5m due east, then 0.80m at 30 degrees north of due east. Beetle 2 also makes two runs; the first is 1.6m at 40 degrees east of due north. What must be (a) the magnitude and (b) the direction of its second run if it is to end up at the new location of beetle 1?

    40 degrees east of due north = 50 degrees

    vector A = 0.5m
    vector B = 0.8m
    vector C = 1.6m

    A = .5i + 0j
    B = (.8cos(30))i + (.8sin(30))j
    C = (1.6cos(50))i + (1.6sin(50))j

    R = 2.35i + 1.78j
    R = [2.35^2 + 1.78^2]^1/2 = 2.95m
    arctan=(1.78/2.35)=37.14 degrees

    Answer should be: (a) 0.84m (b) 79 degrees

    What am I doing wrong here? Am I approaching it wrong?
  2. jcsd
  3. Jan 31, 2005 #2


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    Staff Emeritus
    Science Advisor

    You aren't showing the crucial part of your work! What did you do with vectors A, B, and C after you got them?

    The first beetle's total motion is A+ B, then second's is C so to arrive at the same place the second beetle must go A+B- C.
  4. Jan 31, 2005 #3
    I was adding A + B + C. I see how logically that wouldn't make sense. Thanks I got the answer.
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