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Homework Help: Help with a vector problem

  1. Sep 18, 2004 #1
    Find the horizontal and vertical components of the d = 140 m displacement of a superhero who flies from the top of a tall building following the path shown in Fig. P3.18 where = 35.0°.

    The picture is here http://www.webassign.net/pse/p3-20alt.gif

    Not sure of exactly where to start.
  2. jcsd
  3. Sep 18, 2004 #2
    Start by drawing a triangle and writing what you know on it.
  4. Sep 18, 2004 #3
    well i was able to get the vertical by 140 cos 35, but as I tried 140 sin 35, the answer turned out to be wrong.
  5. Sep 18, 2004 #4
    Remember your trigonometry: what does cos 35 equal in this triangle? What does sin 35 equal?
  6. Sep 18, 2004 #5
    I have a question....do you know what the right answer is...because i think i figured it out......ALSO, I don't know if I'm looking at the problem right...but to me the VERTICAL component (Y) looks to me to be opposite of the angle, which would make the y component 140 sin 35...and the x component is adjacent to the angle, which is 140cos 35
  7. Sep 18, 2004 #6
    That is what I was getting at, hoping motionman would figure it out on his own.
  8. Sep 18, 2004 #7
    Well I know that sin = opposite over hypotenuse, and cos = adjacent over hypotenuse, I tried 140 sin 35 but apparently thats wrong
  9. Sep 18, 2004 #8
    The vertical (y) component should be 140 sin 35, the horizontal (x) component should be 140 cos 35. Make sure your calculator is in degree mode.
  10. Sep 18, 2004 #9
    yep, its in degree mode, and I get an answer of 80.3007 m, however, its wrong for some reason
  11. Sep 19, 2004 #10
    140sin35 = 80.3007, so u are right, what does the answer say in the book?
  12. Sep 19, 2004 #11
    Well its a problem is on webassign.com, and each time I put in that number, it says it is incorrect
  13. Sep 19, 2004 #12
    maybe put negative -80.3007, since it is negative according to the x and y axis on how the diagram is labeled. Other than that, the only thing i can think of is check your significant digits, and how accurate webassign.com wants ur answeres to be.
  14. Sep 19, 2004 #13
    Yep, that did the trick, thanks for that one cinderblock
  15. Sep 19, 2004 #14
    No problem bro
  16. Sep 19, 2004 #15
    I've got another problem thats been stumping me, it goes like this:

    Instructions for finding a buried treasure include the following: Go 77.0 paces at 245°, turn to 130° and walk 110 paces, then travel 100 paces at 162°. The angles are measured counterclockwise from an axis pointing to the east, the +x direction. Determine the resultant displacement from the starting point.

    Now, I've found the x, y components for all three vectors, by doing

    77 cos/sin 245, 110 cos/sin 130, 100 cos/sin 162, and after finding the resultant vector for the x, it turned out to be wrong.
  17. Sep 19, 2004 #16


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    I hate this Web applets, if you put too many numbers it will say wrong...

    try putting -80.30
    Last edited: Sep 19, 2004
  18. Sep 19, 2004 #17


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    Use the components!!

    Sum all the X components and the Y components, and you will have the displacement in X component and Y component.

    Well other than that, let me try

    [tex] \vec{R} = (R_{x}i + R{y}j) m [/tex]

    [tex] R_{x} = 77cos(245) + 110cos(130) + 100cos(162)[/tex]

    [tex] R_{y} = 77sin(245) + 110sin(130) + 100sin(162)[/tex]

    [tex] \vec{R} = (-198.35i + 45.38j) m [/tex]

    [tex] |\vec{R}| = \sqrt{(-198.35)^2 + (45.38)^2} = 203.47 m[/tex]

    [tex] \theta_{R} = 167.11^o [/tex] Counter-Clockwise.
    Last edited: Sep 19, 2004
  19. Sep 19, 2004 #18
    Yeah, I did, I got the resultant vector for the x components and used that as the displacement vector from the starting point
  20. Sep 19, 2004 #19


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    i don't think that's what is asking. It's asking for the Resultant Vector.
  21. Sep 19, 2004 #20
    haha no luck with the 221 or 315 degrees,
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