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: Gravitational Potential Energy of the earth

  1. Mar 23, 2010 #1
    1. The problem statement, all variables and given/known data

    How high above the surface of the Earth must a mass be located so its gravitational potential energy is only 17.00% of its value on the surface?

    2. Relevant equations

    PEg=(-GMm)/r, PElocal= mgy where y is height the object can fall

    3. The attempt at a solution

    I've tried a couple of different things but all my variables cancel out.


    r1/0.17=r2 If I randomly set r1 to be 1 r2= 5.88235 but that doesn't make sense because if you raise an object by 5m it would have a greater PEg

    Any suggestions on where to go?
  2. jcsd
  3. Mar 23, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi kt102188! Welcome to PF! :smile:
    But the radius of the Earth is a lot larger than 1m. :confused:

    (and remember, the question assumes that the PE at ∞ is zero :wink:)
  4. Mar 23, 2010 #3
    Thank you! I was totally thinking of this wrong. Actually using the radius of earth got the right answer.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook