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Speed/Velocity Problem

  1. Sep 27, 2006 #1
    Could someone help me with this, thanks in advance:

    A man can row a boat at the rate of 5.0km/hr in still water. He points the boat directly across a river which flows at the rate of 5km/hr.
    a) Find the boat's final speed
    b) Find the boat's final velocity

    I don't know where to start. Do I use a formula to figure out t then another formula to figure out a and then so on?

    If you can do this, i would appreciate it if you can explain your reasonings, thanks.
  2. jcsd
  3. Sep 27, 2006 #2


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    Regarding b) : the final boat velocity vector equals: [tex]\vec{v}_{B} = \vec{v}_{R} + \vec{v}_{B,R}[/tex]. In words, the total velocity of the boat equals the velocity of the river plus the velocity of the boat relative to the river. So, just add the two known vectors to get the final velocity of the boat. Finding the speed from a) should be simple.
  4. Sep 27, 2006 #3
    Do I have to use 5 for b and r ?
  5. Sep 28, 2006 #4


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    Yes, of course. You know the magnitudes and the directions of the vectors, so you can solve your problem easily.
  6. Sep 28, 2006 #5
    draw a picture of what you are given, then calculate the resultant of the two vectors. This should help you start out
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