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Homework Help: Speed of spacecraft (gravitational force)

  1. Nov 29, 2006 #1
    An unmanned spacecraft is in a circular orbit around the moon, observing the lunar surface from an altitude of 43.0 km (see Appendix F). To the dismay of scientists on earth, an electrical fault causes an on-board thruster to fire, decreasing the speed of the spacecraft by 20.0 m/s.

    If nothing is done to correct its orbit, with what speed (in km/h) will the spacecraft crash into the lunar surface?
    Take the gravitational constant to be 6.673 x 10^-11\cdot {\rm m}^{2}/{\rm kg}^{2}, the mass of the Moon to be 7.35 x 10^22\:{\rm kg}, and the radius of the Moon to be 1.74 x 10^{6}\:{\rm m}.

    We can use equation v = sqrt(Gme)/r))
  2. jcsd
  3. Nov 29, 2006 #2
    Show some work or some reasoning or something that tells us you gave it some thought. Then we can advice you where you may be misunderstanding something.
  4. Nov 29, 2006 #3

    Thank you KoGs for replying to my question. I have finally figure our how to solve the problem. First I have to balance the centripetal force and the centrifugal forces.

    After finding the initial kinetic energy and the energy due to falling I was able to find the speed at which it hits the planet

    Again thank for your help
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