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Relative Velocity of a ship

  1. Sep 17, 2014 #1
    1. The problem statement, all variables and given/known data
    A ship goes from A to B at [tex] v_1=10 km/h [/tex] and from B to A at [tex] v_2=16 km/h [/tex] Find: (1) the average velocity of the ship, and (2) the velocity of the river current.


    2. Relevant equations
    [tex] v_{avg}=(v_1+v_2)/2 [/tex]
    [tex] v_{AC}=v_{AB}+v_{BC} [/tex]

    3. The attempt at a solution
    [tex] v_{Boat}-v_{Current}=10km/h [/tex]
    [tex] v_{Boat}+v_{Current}=16km/h [/tex]
    [tex] v_{Boat}=13km/h, v_{Current}=3km/h [/tex]
    The actual answer for [tex] v_{Boat}=12.3km/h [/tex] Why is that?
     
  2. jcsd
  3. Sep 17, 2014 #2

    Doc Al

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    Staff: Mentor

    What's the definition of average velocity (really average speed)?
     
  4. Sep 17, 2014 #3
    Change in position/Change in time?
     
  5. Sep 17, 2014 #4

    Doc Al

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    Staff: Mentor

    Try total distance / time.

    This only applies to uniformly accelerated motion, which is not what's going on here.
     
  6. Sep 17, 2014 #5
    Ahh... I didn't realise that the equation is only for uniformly accelerated motion. I've got the answer now. Thanks!!
     
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