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!

Energy in Space

  1. Apr 14, 2009 #1
    1. The problem statement, all variables and given/known data

    A 1250kg meteor rock fragment is momentarily at rest at an altitude of 3000km above the surface of Neptune. Neptune has a mass of 1.03x1026kg and a radius of 2.48x107m.

    Determine: how much work is done on the rock by Neptunes Force of gravity as the rock falls to Neptunes surface (I got the answer to this one it was 3.74x1010J

    I need help on: the velocity with which the rock strikes Neptunes surface

    Not sure where to start with this one.
     
  2. jcsd
  3. Apr 14, 2009 #2
    If you can find the gravity on Neptune, you can use conservation of energy to determine it's velocity.
     
  4. Apr 14, 2009 #3
    so:
    W=Ek
    3.74x10^10j=1/2mv^2
    3.74x10^10j=1/2(1250kg)v^2
    v= (square root of) 3.74x10^10j/1250kg
    = 7.7X10^4

    But the answer says 7.7X10^3

    Where did i go wrong?
     
  5. Apr 14, 2009 #4
    The 1/2 magically disappeared. :) You just forgot to multiply by 2, but you got essentially.
     
  6. Apr 14, 2009 #5
    i screwd up there... when i take half of the 1250kg i get the answer above.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook