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!

Graviational acceleration given mass and radius

  1. Oct 31, 2012 #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. Oct 31, 2012 #2

    Ibix

    User Avatar
    Science Advisor

    Two rules for doing physics problems:
    1 - Check your units
    2 - Never put in a hard number until you can't avoid it

    You're tripping over rule 1 - which of your numbers is not in SI units?

    Remember rule 2 when you're doing the question proper. The approach I suspect you are about to use will work, but there is a way to do it without needing to know either the Earth's mass or radius.
     
  4. Oct 31, 2012 #3
    Thanks, I actually went back and redid it later and got the answer I was looking for.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook