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!

Buoancy force question

  1. Mar 5, 2010 #1
    1. The problem statement, all variables and given/known data
    A cube made from iron has sides equal to 20cm/side. The density of iron is 7860kg/m^3. The cube is completely submerged in water; the density of water is 1000kg/m^3. What is the buoancy force acting on the cube.

    2. Relevant equations
    W(DL)= (D(L))(V)(g)

    3. The attempt at a solution
    W(DL)=(1000kg/m^3)(8000cm^3)(10m/s^2) =8x10^7 Neutons
    Im not sure if this answer is correct ????
  2. jcsd
  3. Mar 5, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    Take care of your dimensions. You're using the density in kg per meter^3, but volume in cm^3.
    1 Newton is 1 [itex]kg m s^{-2}[/itex] You can get the right units from there.
    When in doubt, always use SI-units.
  4. Mar 5, 2010 #3


    User Avatar
    Homework Helper

    Force of buoyancy = weight of the water displaced by the cube. How can that small cube of water weight 8x10^7 newtons?

    Think, what is your weight? less or more than 8x10^7 N? Your average density is also very close to 1000 kg/m^3. Are you bigger or smaller than that 20x20x20 cm^3 cube?

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Buoancy force question Date
Magnitude of the average force during a collision Yesterday at 12:21 PM
Buoancy volume question Nov 16, 2016
Buoancy (block floating in water) Sep 15, 2008
Buoancy / Archimedes Principle Jan 19, 2005
Buoancy, old exam question Jul 25, 2004