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: Buoyancy without density of fluid

  1. Nov 3, 2008 #1
    1. The problem statement, all variables and given/known data
    A ball of mass m_b and volume V is lowered on a string into a fluid of density rho_f. Assume that the object would sink to the bottom if it were not supported by the string.
    What is the tension T in the string when the ball is fully submerged but not touching the bottom?
    It claims that rho_f is not needed in the part representing buoyancy
    2. Relevant equations

    I think it should be:
    T=Fg - B
    where T is the force of tension and B is the buoyancy force.
    therefore, T=mg - rho_f*V*g

    how can you not use rho_f in calculating the buoyancy force?

    3. The attempt at a solution
  2. jcsd
  3. Nov 3, 2008 #2


    User Avatar
    Science Advisor
    Homework Helper

    You need the density, unles you are going to quote the answer in terms of density.
    Imagine the fluid is air and a metal ball, if you change the fluid to water - then the tension in the string is going to change.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook