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: A question about Newton's Law of Universal Gravitation

  1. Dec 18, 2007 #1
    1. The problem statement, all variables and given/known data
    The gravitational force between two shperes is 2.50x10^-8. Their centers are 105 cm apart. The larger sphere has a mass of 8.20 kg. Find the mass of the smaller sphere.

    2. Relevant equations

    3. The attempt at a solution
    d² x F=Gm1m2/d² x d²

    m2=((2.50x10^-8 N)(105² cm))/((6.67x10^-11 Nm²/kg²)(8.20 kg))
    m2=5.04x10^5 kg

    That can't be right because the missing mass is supposed to be smaller than 8.20 kg. Did I move the equation around right?
  2. jcsd
  3. Dec 18, 2007 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Are you mixing the units cm and m inappropriately?

    - Warren
  4. Dec 18, 2007 #3
    Okay, I forgot to convert cm to m.

    But using d=1.05 meters, I get 50.4 kg as my answer. It's closer, but still too large. :frown:
  5. Dec 18, 2007 #4


    User Avatar

    I agree with your result.

    By "smaller" sphere they may have meant smaller in size, not necessarily smaller in mass.
  6. Dec 18, 2007 #5
    So far though, we've only used mass for those problems.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook