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Hard time getting the volume of the boat

  1. Nov 22, 2003 #1
    I am stuck on this problem...

    A rowboat measures 4ft wide by 10ft long. How much (in inches) will the boat sink into the water when two 200 lbs me get into the boat?

    A: I am having a hard time getting the volume of the boat…does anyone have a suggestion?

    This was my plan:
    W boat= volume * density of a wood
    W men= 400lb = 181.57kg * p.8 N/kg= 1779.39N
    F bouy= W water = mg=pVg= 1000kg/m^3 * volume displaced *9.8 N/kg =

    F lift = F buoy – W boat – W men =

    I don’t even know if I am headed in the right direction…..Can anyone help?
    Thank for the help in advance.
  2. jcsd
  3. Nov 23, 2003 #2


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    Science Advisor

    Your basic idea is good but why are you converting from
    English units to metric? I know metric is easier to use, but when you are given everything in English to begin with...

    OUCH!! I had spent about 10 minutes on this when suddenly the light dawned! The problem asks for the depth the boat SINKS when the two 200 pound men get into the boat. You DONT NEED to find the weight of the boat itself- that's already accounted for by the fact that the boat is floating already before the men get in. You only need to find how much MORE it sinks!

    You are given that the weight of the men is 400 pounds, total. The boat will sink (further) into the water until it displaces water equal in weight to the weight of the men: The volume of water displaced is 4*10*h where h is the depth (in feet) the boat sinks. Multiply that by the density of water (in pounds per cubic foot!) and set it equal to 400.
  4. Nov 23, 2003 #3
    Thank you....that really helped.
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