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 Acceleration given mass and radius

  1. Apr 9, 2014 #1
    1. The problem statement, all variables and given/known data
    If you lived on a planet with five times the mass of Earth and twice the radius, what would be the gravitational acceleration at the surface of your planet?


    2. Relevant equations
    GM/r^2
    Mass of Earth = 6.00*10^24 kg
    Radius of Earth = 6.38*10^3 km


    3. The attempt at a solution
    So, when I started out doing this, I quickly plugged in earth's radius (in m), mass (in kg) and the gravitational constant just to make sure it came out at 9.8 because I know that's what Earth's gravitational acceleration from the surface is, but none of the answer I get are even close. I can't even get this right and I still have to do the actual problem (using 5x the mass and 2x the radius).
     
  2. jcsd
  3. Apr 9, 2014 #2

    SteamKing

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Instead of making us guess where you went wrong, how about posting your work?
     
  4. Apr 9, 2014 #3

    BiGyElLoWhAt

    User Avatar
    Gold Member

    it does work. we did it the other day sitting around.
    try
    GM/r^2
    Mass of Earth ≈ 5.97*10^24 kg
    Radius of Earth ≈ 6.38*10^3 KM = 6.38*10^6 m
    G≈ 6.67 × 10^-11

    [itex]\frac{M_{earth}}{r_{earth}^2}G ≈ \frac{5.97*10^{24}}{6.38*10^{12}}*6.67*10^{-11}[/itex]
    [itex]=\frac{5.97*6.67*10}{6.38} ≈9.805[/itex]
     
  5. Apr 9, 2014 #4

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    2016 Award

    It's worth persevering to get that right, but you don't need it for this question.
    You can solve it just by taking g = 9.8m/s2 for Earth and adjusting it. What effect will 5 times the mass have on that? What effect will twice the radius have?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted