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Vectors problem help please

  1. Sep 8, 2012 #1
    1. The problem statement, all variables and given/known data
    A man walks 5 m at 37degrees north of east and then 10 m at 60degrees
    west of north. What is the magnitude and direction of his net
    displacement

    The answer is around 9.3m at around 120 degrees angle on the +x axis

    2. Relevant equations
    none


    3. The attempt at a solution
    http://img825.imageshack.us/img825/2570/vectors2.png [Broken]

    I have no idea what to do after I plot out the vector and connect tip to head. Can someone explain to me how to solve for vectors effectively?

    Thank you
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Sep 8, 2012 #2

    phinds

    User Avatar
    Gold Member
    2016 Award

    One way to go after it is to draw right triangles and use them to find the end points in XY coordinates of what you have in the drawing. See if you can figure out what I'm talking about.
     
  4. Sep 8, 2012 #3
    Another way is to resolve the vectors along x and y axis

    5m 37degrees north of east can be written as cos(37)*5 along x axis and sin(37)*5 along y axis

    similarly do it for other vector..

    now add components along x and y axis seperately and get new measurements along x and y axis

    now use x2+y2 = (magnitude of resultant)2
    for magnitude

    and arctan(y/x) for direction of resultant vector.(x and y are values of new measurements along x and y axis) (angle obtained is the angle from +ve x axis)
     
  5. Sep 8, 2012 #4
    You really surprise me. You can't figure out how to obtain the distance between two points given their coordinates, yet you advise others precisely on how this is done.
     
  6. Sep 8, 2012 #5
    Did i make a mistake??
     
  7. Sep 9, 2012 #6
    No you did not. That's why I am surprised. Why can't you apply this same knowledge to your problem about the moment of inertia?
     
  8. Sep 9, 2012 #7
    Basically i got it

    But pls help me with the double integration

    i mean how is it done??
     
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