1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

A guy and his raft

  1. Dec 15, 2003 #1
    Okay, I've worked this problem and have what I think is the correct answer...I just want to get a second opinion because I am a little bit unsure.

    A raft is constructed of wood having a density of 600 kg/m^3. It's surface area is 5.8 m^2, and its volume is .60 m^3.

    - A 80 kg man jumps on the raft. After a while, the man + raft system becomes stable. What is the % of the raft submerged?

    My work:

    I assume that at equilibrium the weight of the raft + man must equal the bouyant force.

    I use mass = (density)*(volume) to get the mass of the raft (360 kg) then add 80 kg to get the new mass, 440 kg. Now I take that mass times gravity to get the weight. And set that equal to the bouyant force of (density of water)*(volume displaced)*(gravity). It looks like this:

    (440)g = (1000)(V)(g)
    so 440/1000 = v
    that gives me .44 as the displaced volume of water.
    This is where my question arises. Is 44% the amount of the raft submerged? Or do I then need to divide the displaced volume by the volume of the raft (.44/.6) to get .73 or 73%?

    If I've worked it wrong please let me know but I think I've done it correctly...I'm just unsure which of the 2 answers is the correct one.

    Thanks!
    -edge
     
  2. jcsd
  3. Dec 15, 2003 #2

    NateTG

    User Avatar
    Science Advisor
    Homework Helper

    It's asking for the percentage of the raft that is submerged, not the volume, so the answer is 73%.

    If you keep track of units, you can check because percentages should always be unit-less.
     
  4. Dec 15, 2003 #3
    Awesome, thanks. Silly me, simple errors...they kill me. Thanks for the help!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: A guy and his raft
  1. A Dog on a Raft (Replies: 2)

  2. Buoyancy of a raft (Replies: 11)

  3. Raft buoyancy problem (Replies: 14)

Loading...