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Speed of comet

  1. Sep 27, 2007 #1
    A comet is in an elliptical orbit around the Sun. Its closest approach to the Sun is a distance of 4.5 1010 m (inside the orbit of Mercury), at which point its speed is 8.9 104 m/s. Its farthest distance from the Sun is far beyond the orbit of Pluto. What is its speed when it is 6 1012 m from the Sun? (This is the approximate distance of Pluto from the Sun.)

    i have no clue how to find the speed given only the distances and the other speed
     
  2. jcsd
  3. Sep 27, 2007 #2

    Doc Al

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    Staff: Mentor

    Hint: What's conserved?
     
  4. Sep 27, 2007 #3
    see thats what i dont know...my guess would be kinetic energy is conserved but i dont really know...i suck at physics i never know whats going on
     
  5. Sep 27, 2007 #4

    Doc Al

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    Mechanical energy (kinetic energy + gravitational potential energy) is conserved.
     
  6. Sep 27, 2007 #5
    so how do i use this in an equation can i set it up as a proportion
     
  7. Sep 27, 2007 #6

    Doc Al

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    Initial total energy = final total energy. You'll need to know how to calculate gravitational PE.
     
  8. Feb 19, 2009 #7
    What if you dont know the mass of the comet, because dont you need this to use the gravitational PE?
     
  9. Feb 19, 2009 #8

    Doc Al

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    You don't need the actual mass. Just call it "m" and see what happens.
     
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