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Homework Help: Gravitation Help

  1. Oct 1, 2006 #1
    I'm having trouble distinguishing the values of the components in the gravitation equation for the following problem:

    Here is how I approached it -

    The equations I will be using are:
    F = G*M*m/r^2
    [tex]KE=\frac{1}{2}m v^2[/tex]

    So first off, I solved for the force using the gravitation equation -
    G constant = 6.67e-11 Nm^2/kg^2
    M (of star) = 1.14*10^32 kg
    m (of rocket) = 1.25*10^6 kg
    r = now this is where my question is. :yuck: The problem says that r is the distance between the centers of the two bodies. So, I assumed that it's the radius given 3.48*10^9 m added to the distance between the rocket and the star (1.85*10^11 m) and then squared. Is this correct? Or is it just supposed to be the radius of the star squared?

    After that first assumption, I plugged the force value I found into
    [tex]W=F*cos(\theta)(delta x)[/tex]
    which brings me to the second question. Is the delta x value = 1.85*10^11 m?

    Then, I plugged that value I found for W into [tex]KE=\frac{1}{2}m v^2[/tex], where m=1.25*10^6.

    Is this a correct approach and did I assume anything wrong?

    Thanks in advance!
    Last edited: Oct 1, 2006
  2. jcsd
  3. Oct 2, 2006 #2


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    Homework Helper

    The gravitational force is a function of r. Which means that you need to integrate in order to find the work done by this force on the rocket in pulling it towards the star.
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