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: Really stuck on a Gravitation Question

  1. Nov 17, 2008 #1
    1. The problem statement, all variables and given/known data

    What minimum energy is required to raise a 1.7e3 kg vehicle from the surface of the moon to a height of 5.22e6 m?

    2. Relevant equations

    Ep= -G(m1m2)/r

    3. The attempt at a solution

    Ep(initial)= -6.67e^-11(1.7e^3 x 7.35e^22)/1.74e^6 = -4789750000

    Ep(final)= -6.67^-11(1.7e3 x 7.35e^22)/6.96e^6= -1197437500

    I have tried subtracting the final by the initial, but I am not getting the correct answer of 3.6e^9 J.
  2. jcsd
  3. Nov 17, 2008 #2


    User Avatar
    Homework Helper

    Hi grantP,

    What are you getting? It looks to me like if you do Ep(final) - Ep(initial) you do get 3.6 x 109J.
  4. Nov 18, 2008 #3
    oh......hmmmm i must have mixed up my signs....and doing 4 straight hours of physics homework probably didnt help.....looking back at it 4 hours later I was probabaly so delerious haha.

    Well anyways thanks for the help on my threads.
  5. Nov 18, 2008 #4


    User Avatar
    Homework Helper

    Right, I understand completely about how too much work can make you start seeing things. Glad to help!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook