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!

Gravitational force

  1. Aug 4, 2009 #1
    1. The problem statement, all variables and given/known data

    When the distance separating two masses, M and m, is 1.2 x 10^10 m, the gravitational force of attraction is 5.0 N. If the mass of M becomes 3M and the separation distance becomes
    2.4 x 1010 m, what will be the force?


    2. Relevant equations
    Fg=MaMb/r^2


    3. The attempt at a solution
    since i have r and Fg (first part of question) i tried solving for the masses. but how do i solve for both when i need at least one to solve the other/??
     
  2. jcsd
  3. Aug 4, 2009 #2

    Pengwuino

    User Avatar
    Gold Member

    You're missing the gravitational constant in your equation. I suggest setting up a ratio between the two forces and see what happens.
     
  4. Aug 4, 2009 #3
    huh? im still kinda confused..
     
  5. Aug 4, 2009 #4

    Pengwuino

    User Avatar
    Gold Member

    You know : [tex]F_1 = \frac{{GM_1 m_1 }}{{r_1 ^2 }}[/tex] and that [tex]F_2 = \frac{{GM_2 m_2 }}{{r_2 ^2 }}[/tex].

    What do you get when you divide the second equation by the first, that is: [tex]\frac{{F_2 }}{{F_1 }}[/tex].

    You know:

    [tex]\[
    \begin{array}{l}
    M_2 = 3M_1 \\
    m_1 = m_2 \\
    \end{array}
    \]
    [/tex]

    along with the actual initial force, [tex]F_1[/tex]. You can solve for the ratio of forces which will tell you what [tex]F_2[/tex] is.
     
  6. Aug 5, 2009 #5
    or, use this EASIER way :

    for the first condition, and the second condition, the gravitational constant is always the same.
    [tex]G=G[/tex]

    You have known what the value of F is :
    [tex]F=\frac{GMm}{r^2 }[/tex]
    and, the value of G is :
    [tex]G=\frac{Fr^2 }{Mm}[/tex]

    you can make it like this :
    [tex]G=G[/tex]
    [tex]\frac{Fr1^2 }{M1m1}=\frac{Fr2^2 }{M2m2}[/tex]
    substitute the variable ( like M2 to 3 Mi ) and you can eliminate the variable. At last, there will be an equation like F2 = k.F1
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Gravitational force
  1. Gravitation Force (Replies: 4)

  2. Gravitational force (Replies: 1)

  3. Gravitational force (Replies: 2)

  4. Gravitational force? (Replies: 2)

Loading...