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Vector problem

  1. Sep 14, 2011 #1
    Check out picture for problem...

    My solution:

    Vector pointing towards girl: I named it vector A, Boy Vector B

    R = A + B + unkC = (15,0)

    A = Ax + Ay = (10,0)
    B = Bx + By = (0,5)
    C = Cx + Cy = (?,?)

    Total = 10,5
    Cx = 5 Cy = -5

    (50)^(1/2) = 7 = C

    The answer however was 14
     

    Attached Files:

    Last edited: Sep 14, 2011
  2. jcsd
  3. Sep 14, 2011 #2
    erm ,

    this is how to think

    if you want the resultant of forces A B C to be 15 upwards, then that means your total horizontal forces are 0 , while your total vertical forces = 15 upwards

    since your current set-up has 10 to the right and 5 to the top, this means that you need 10 to the left to make your total horizontal forces are 0. likewise, you need 10 to the top so that total total vertical forces = 10+5 = 15 upwards

    so your "additional force C" comprise of 10 to the left and 10 to the top, which means the resultant of C is

    C2 = 102 + 102
    C = 14.1 N , directed diagonally to the top-left direction
     
  4. Sep 14, 2011 #3
    oh, in case you want to put it mathematically, it will be something like this

    take right and upwards direction as positive,

    solving for x-components,

    total x = B + Cx = 0
    +10 + Cx = 0
    Cx= -10 , this tells you Cx is directed to the left, because we took right as positive

    solving for y-components,

    total y = A + Cy = 15
    5 + Cy = 15
    Cy = +10, this tells you Cy is directed upwards , because we took upwards as positive

    so resultant C2 = Cx2 + Cy2 --> pythagoras theorem

    so C = 14.1

    for direction, if we take angle T to be between the x-axis and the resultant C, then

    tan(T) = Cy / Cx = 10/10 =1
    thus, T = 45 degrees
     
    Last edited: Sep 14, 2011
  5. Sep 14, 2011 #4
    Thank you!
     
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