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Mass of a comet problem

  1. Mar 25, 2008 #1
    [SOLVED] Mass of a comet problem

    On July 4, 2005, the NASA spacecraft Deep Impact fired a projectile onto the surface of Comet Tempel 1. This comet is about 9.0 {\rm km} across. Observations of surface debris released by the impact showed that dust with a speed as low as 1.0 {\rm m/s} was able to escape the comet.

    1)Assuming a spherical shape, what is the mass of this comet? ( The escape speed for an object at the surface of Earth is 11.2 {\rm km/s} ).

    2)How far from the comet's center will this debris be when it has lost 70 {\rm \%} of its initial kinetic energy at the surface?

    I have absolutely no idea what to do. any help would be appreciated.
     
  2. jcsd
  3. Mar 25, 2008 #2
  4. Mar 25, 2008 #3

    berkeman

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    Staff: Mentor

    Thread moved to Homework Help forums. Joe, start by telling us about the term "escape velocity", and how it relates to gravitational attraction.
     
  5. Mar 25, 2008 #4
    the only thing i know is that the escape velocity for the earth is equal to the square root of (G*mass of earth/radius of earth). our teacher really doesnt explain anything.
     
  6. Mar 25, 2008 #5
    maybe i could use that and compare it to the escape velocity of the comet somehow but i don't know how. its just a really confusing problem because not much is explained.
     
  7. Mar 25, 2008 #6

    berkeman

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    Here's a reference on escape velocity. This should give you all that you need to solve the question. Read through this, and then post your work here if you still need help.

    http://en.wikipedia.org/wiki/Escape_velocity
     
  8. Mar 25, 2008 #7
    ok. solving for M =v^2*r/(2G) and plugging in i got 3.37 x 10^13. does that sound about right?
     
  9. Mar 25, 2008 #8

    berkeman

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    What are your units? What did you get for part B) ?
     
  10. Mar 25, 2008 #9
    my units are in kg.
     
  11. Mar 25, 2008 #10
    thanks i got it.
     
  12. Apr 16, 2008 #11
    bump, I have no idea how to get part b
     
  13. Apr 17, 2008 #12

    berkeman

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    Staff: Mentor

    What did you get for the answer for the first part? What can you tell us about the relationship between KE, PE, and total energy?
     
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