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What's their velocity relative to the water?

  1. Oct 11, 2010 #1
    1. The problem statement, all variables and given/known data

    Boat moving at 2.8 m/s [fwd] relative to water (VBW)
    Tourists walking on deck at 1.1 m/s relative to deck (VPB)

    Determine their velocity relative to the water if they are walking towards the starboard (right side of ship).

    2. Relevant equations

    VPW = VPB + VBW

    3. The attempt at a solution

    VPW = 1.1 m/s [R] + 2.8 m/s [fwd]

    VPB = 1.1 m/s: x-dir = 0 and y-dir = 1.1 m/s
    VBW = 2.8 m/s: x-dir = 2.8 m/s and y-dir = 0

    VPW = ??: x-dir 2.8 m/s y-dir = 1.1 m/s

    So do I just draw a graph? Like, 2.8 in magnitude along the positive x-axis, and then 1.1 in magnitude up (or how would I think about this? like how would I know where to draw the vectors and which direction etc. in a more complicated question?)

    and just

    c = sqrt(a2 + b2)
    c = 3.01 m/s
    VPW = 3.01 m/s

    Then how do I find the direction of VPW?

    [tan-1(1.1/2.8)] = [E 21.45 N] or [21.45 N of the horizontal] or what? since the question doesn't use direction

    Also, how many significant digits should I leave my answers to (both velocity and direction)?
    Last edited: Oct 11, 2010
  2. jcsd
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