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Relative Motion With Vectors

  1. Feb 25, 2016 #1
    1. The problem statement, all variables and given/known data
    A ball rolls with a velocity of 14 mm/s [W] on a board that is being pulled [E 60o N] at 20.0 mm/s. What is the velocity of the ball relative to the floor?

    b = ball
    x = board
    f = floor
    2. Relevant equations
    V_bf = V_bx + V_xf

    3. The attempt at a solution
    I tried to work through this question by drawing it on a Cartesian grid and by drawing out the vectors. I used trigonometry on the triangle to figure out the component of V_xf horizontally, and then plugging V_xf into the V_bf = V_bx + V_xf equation. The answer I got was 4 mm/s W, but is was incorrect. I am not sure where I went wrong.
     
  2. jcsd
  3. Feb 25, 2016 #2

    haruspex

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    Strangely, neither am I. Why might that be?
     
  4. Feb 28, 2016 #3

    ehild

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    The velocity vector has both westward and northward components.
    Do you mean 60° East of North as the direction of velocity of the board?
     
  5. Feb 29, 2016 #4

    HallsofIvy

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    60 degrees east of north would be written as N60E. E60N is not a standard notation ("standard notation" goes from N or S first) but I would interpret it as "60 degrees north of east" which would be the same as "30 degrees east of north" or N30E. If you want someone to explain "what you did wrong", you will have to tell us what you did!
     
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