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Spacecraft Deep Impact - Comet's mass

  1. Apr 16, 2008 #1
    1. The problem statement, all variables and given/known data

    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. Relevant equations
    I know that for part a it is V=sqrt((2GM)/r)

    but then how I calculate the lost kinetic energy.


    3. The attempt at a solution
     
  2. jcsd
  3. Apr 17, 2008 #2

    Hootenanny

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    You know that it is 70% of it's intial value...
     
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