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Projectile Motion #3

  1. Oct 25, 2006 #1
    A boat can travel at a speed of 3.4 m/s in still water. A river that is 160 m wide has a current that flows 1.3 m/s due West.

    a) If the boat points its bow directly across the river, how fast does the boat travel relative to the shore?
    3.64 m/s
    b) How long will it take to cross the river?
    47.0588 s
    c) Fow far downriver will it land (the distance on the bank from the point directly across from the starting point to the landing point)?
    m
    d) At what angle should the boat be pointed in order to arrive at a point directly across from the starting point? Assume North is directly across the river.
    ° E of N
    e) How long does that take?
    s

    I got A and B but I don't know how to setup C -- Any ideas?
     
  2. jcsd
  3. Oct 25, 2006 #2

    Doc Al

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    Staff: Mentor

    How fast is the boat going downstream? How far does it get in the time it takes to cross the river?
     
  4. Oct 25, 2006 #3
    He's moving 3.4 + 1.3 so 4.5 m/s downstream and it would take him 47.0588 s to get across according to B.
     
  5. Oct 25, 2006 #4
    Doc?! You there?
     
  6. Oct 26, 2006 #5

    Doc Al

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    Staff: Mentor

    No, he's moving 3.4 m/s across and 1.3 m/s downstream. (He points the boat directly across, which gets him across in the quickest time possible but requires him to move downstream along with the current. If he wants to go straight across the river without being dragged by the current, he'll have to point the boat at an angle--that's part d.)
    Right, so how far does he get downstream in that time?
     
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