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Homework Help: Conservation of Momentum of a boat and women

  1. Feb 13, 2010 #1
    1. The problem statement, all variables and given/known data
    I'm getting fairly frustrated seeing as I've been working on this 'easy' problem for several hours yet still can't get the correct solution. The problem is as follows:
    A 180 lb- man and a 120-lb woman stand side by side at the same end of a 300-lb boat, ready to dive, each with a 16 ft/s velocity relative to the boat. Determine the velocity of the boat after they have both dived if the woman dives first.

    2. Relevant equations
    Total initial momenta=total final momenta

    3. The attempt at a solution

    First, the woman dives.
    0=480(v) +120(16) b=-4 ft/s

    Second, the man dives:
    (300+180)(-4)=(180)(16)+300(Vf) I keep getting Vf=-16, the book says it is supposed to be -9.2. Can anyone tell me what I am doing wrong?
  2. jcsd
  3. Feb 13, 2010 #2
    You have used velocity of man relative to boat in an eqn. along with velocities w.r.t ground?
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