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Homework Help: Simple,quick relative velocity question?

  1. Sep 9, 2009 #1
    Hello I'll make it quick

    Boat is travelling at 10m/s the sea is travelling at 5m/s. What is the speed of the boat relative to the sea and why?

    Through vectors I worked it out to be 10m/s(not sure) but shouldn't it be five because if a person is standing in the sea and sees the boat it would be travelling at 5m/s.

    The ship relative to the ground is 15m/s right.

    Thank you!!
  2. jcsd
  3. Sep 9, 2009 #2


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    Homework Helper


    B/S= Boat relative to Sea

    I assume if there is a diagram it looks like this

    --------> boat
    ----> sea

    [tex]\vec{v}_{B/S}=\vec{v}_B-\vec{v}_S = 10-5=5 m/s[/tex]

    So the boat 'feels' as if it is traveling at 5m/s instead of 10m/s
  4. Sep 10, 2009 #3
    Thank you for your help. Isn't it 15m/s-10m/s. That is where my confusion lies. Isn't the boat relative to the ground 15m/s(someone in the shore would feel the boat travelling at 15m/s). When you are in the boat do you feel the resultant velocity or the actual velocity.
  5. Sep 10, 2009 #4

    Doc Al

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    Staff: Mentor

    With respect to what? The water or the ground? And in what direction?
    Presumably with respect to the ground.
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