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

    alphysicist

    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

    alphysicist

    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