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!

Potential energy turned into kinetic

  1. Sep 19, 2014 #1
    1. The problem statement, all variables and given/known data
    We have an object with much smaller mass than compared to the sun.
    This object is at rest when released at 1AU from the sun. After a week how far is the mass from the sun.
    3. The attempt at a solution
    So I look at the gravitational potential energy and set it equal to kinetic energy.
    [itex] \frac{-GMm}{r}=\frac{m(v)^2}{2} [/itex]
    the v should be an r dot. now I take the square root of both sides. and then multiply both sides by dt then move the r from the left side to the right side and then integrate bothe sides. this will give me r(t). and then for the bounds I use r=1au and then I can solve for r final. after using t=0 and t=1 week for the time. i will put the time in seconds. this seems somewhat reasonable.
     
  2. jcsd
  3. Sep 19, 2014 #2

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Why would the kinetic energy equal the gravitational potential? There is nothing saying this has to be the case (furthermore, the potential is only defined up to an arbitrary constant) and in particular it does not make sense in your case since the potential is strictly negative and kinetic energy non negative.

    You can go one of two ways:
    1. Write down the force equation and solve for r as a function of time.
    2. Use conservation of energy (this will save you one integration)
     
  4. Sep 20, 2014 #3
    for the force equation would I use F=ma and set it equal to the gravitational force.
    For conservation of energy would I say that kinetic plus potential is a constant.
     
  5. Sep 20, 2014 #4

    Orodruin

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    Yes, both would be correct approaches so I suggest you try doing either of those and return with the result. For the second approach, remember that ##v = -\dot r## and (for both approaches) that ##v(t=0) = 0## and ##r(t=0) = R_\oplus##.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Potential energy turned into kinetic
Loading...