1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Basic Buoyant Force HW Question

  1. Feb 28, 2008 #1
    [SOLVED] Basic Buoyant Force HW Question

    First time doing this, so bare with me:)

    1. The problem statement, all variables and given/known data

    A 53kg girl dives off a raft 4m square floating in a freshwater lake. By how much does the raft rise?

    Density of water = 1000kg/m^3

    Use the equation for buoyant force. Then solve the equation for V.

    Of course, volume = L x W x H.

    g = 9.8 m/s^2

    Fb = weight of girl in Newtons

    3. The attempt at a solution

    My teacher gives us the equation for buoyant force as Fb = (density)(volume)(acc.due to gravity).

    The answer is to be given in cms (centimeters).

    Fb = (1000)(???)(9.8)

    I am trying to get the volume, knowing that there is 4m squared. I am just missing the height.

    Thanks for any ideas...
  2. jcsd
  3. Feb 28, 2008 #2
    Okay, just looking over my notes one more time. My teacher said to use the weight of the girl (53kg) to equal Fb.

    How do I convert 53kg to Newtons? I can use online calculators, but that is not helping me learn. It looks like it is 9.8 x 53 = 519.4 Newtons

    So I should be getting Fb = (1000)(V)(9.8) or 519.4 = (1000)(V)(9.8).

    I just have to solve for V it looks like.
    Last edited: Feb 28, 2008
  4. Feb 28, 2008 #3
    I am trying to solve for volume. I have 4m ^2 given in the problem.

    Okay, the formula to work from is:

    1. Fb = (Density in kg/m^3)(Volume)(Acc. Due to Gravity)
    2. 519.4 = (1000 kg/m^3)(V)(9.8 m/s^2)
    3. 519.4 = 9800V
    4. Volume = 18.87 (units?)

    Is this correct so far?

    How do I convert this to centimeters.?
  5. Mar 2, 2008 #4

    Shooting Star

    User Avatar
    Homework Helper

    How do you get 4 from 3?

    Are you able to understand the concept behind what you are doing? Refer to this similar problem in PF and see.

  6. Mar 17, 2008 #5
    Sorry for the late response. I figured out the problem.

    The professor made a typo in our question, and she corrected it. I solved it very quickly after that.

    Thanks anyways!
  7. Oct 16, 2011 #6
    Re: [SOLVED] Basic Buoyant Force HW Question

    if Buoyant force equals to weight of girl in Newtons
    Fb = W
    (Density in kg/m^3)*(Volume)*(Acc. Due to Gravity) = (mass)*(Acc. Due to Gravity)
    (Density in kg/m^3)*(Volume) = (mass)

    Volume = A.h

    (Density in kg/m^3)*(A.h) = (mass)

    h = (mass) / (Density in kg/m^3)*(A) = 0.01325 m = 1,325 cm

    Last edited by a moderator: Apr 26, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook