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Solving an Equation using the Gravitational Constant

  1. Feb 27, 2007 #1
    1. The problem statement, all variables and given/known data
    Why, in the second step of the question, is 0.001 added to the right side?

    Part 2. In the equation Ve = sqrt 2(6.6742 x 10^-11 N m^2 / kg^2 (12.1kg))/0.106780959m

    I'm trying to calculate the escape velocity of an object, and have figured out everything up to this point. Now, I have no idea how to procede. Do I cancel things out? Do I add a number to both sides?


    2. Relevant equations
    [​IMG]




    3. The attempt at a solution

    For the first part, I would guess that it is simply to... well I have no idea...
     
  2. jcsd
  3. Feb 27, 2007 #2

    cristo

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    200 is multiplied by 0.001 to convert it from grams into kilograms, since there are 1000g in 1kg-- does that answer your question?
    I don't get what you mean by this!
     
  4. Feb 27, 2007 #3
    The formula to calculate escape velocity is:

    Ve = sqrt 2(mu)/r

    Where r is the distance from the denter of the object to be escaped from, and mu is the Gravitational Constant multiplied by the mass of the object to be escaped from.

    All sai and done, this gives an equation of: Ve = sqrt 2(6.6742 x 10^-11 N m^2 / kg^2 (12.1kg))/0.106780959m

    What would be the next step in solving this?
     
  5. Feb 27, 2007 #4

    cristo

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    You just need to check that the units cancel to give a unit of velocity (noting that N=kg m s-2), then compute the numerical answer.
     
  6. Feb 27, 2007 #5

    So would the next step be: Ve = sqrt 2(6.6742 x 10^-11 kg m/s^2 m^2/kg^2 (12.1kg)/0.106780959m ?

    If not, then what?
     
  7. Feb 28, 2007 #6

    cristo

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    Yes, now check that the units cancel and compute the numerical answer.

    Personally, I think the method of keeping the units in during the calculation is very confusing, and that you should convert everything into SI units before plugging into the equation. But ,if that's how you've been taught to answer the question, then I guess you should do it that way.
     
    Last edited: Feb 28, 2007
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