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Projectile moving from Earth's surface

  1. Nov 7, 2007 #1
    A projectile is shot directley away from Earth's surface. Neglect the rotation of Earth. What multiple of Earth's radius RE gives the radial distance a projectile reaches if (a) its initial is .500 of the escape speed from Earth and (b) its initial kinetic energy is .500 of the kinetic energy required to escape Earth? (c) What is the least initial mechanical energy required at launch if the projectile is to escape Earth?

    I think i got (a) and (b) but i need help on (c).
    I don't understand how to complete the problem without knowing the mass of the projectile.

    Please help.
  2. jcsd
  3. Nov 7, 2007 #2


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    If you got a) and b) then you don't need much help from me. Just express c) in terms of m. Where you don't know m. Leave it as a variable.
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