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Homework Help: Conservation of momentum problem regarding a missing mass of a ship!

  1. Mar 5, 2013 #1
    1. The problem statement, all variables and given/known data

    After a malfunction, an astronaut escapes from a doomed spacecraft by using an escape pod that is blown off of the ship. The small explosion sends the pod flying away at 34.9 m/s, while the main ship moves in the opposite direction at the speed of 1.89 cm/s. If the combined mass of the astronaut and pod is 1270 kg, what is the mass of the doomed spacecraft?

    2. Relevant equations

    Conservation of Momentum:

    m1u1+m2u2 (initial) = m1v1+m2v2 (final)

    3. The attempt at a solution

    I believe that conservation of momentum is the correct principle to use here, but I am unsure how to solve for the spaceship's mass because of the missing initial velocity. Could someone help me out? Thanks!
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Mar 5, 2013 #2


    User Avatar
    Science Advisor
    Gold Member

    Hi there!

    The initial velocity was meant to be 0 for both the ship and the pod.
    Those velocities provided are for after the separation, relative to their mutual centre of mass.
  4. Mar 5, 2013 #3
    If the spaceship and pod before the launch had 0 momentum to their mutual centre of mass, the conservation of momentum says:

    the pod and spaceship must have right after the launch 0 momentum to their mutual centre of mass. So you have 4 variables ( as intial velocities were both 0 ) after the launch; ( mass and velocity of spaceship and pod ).
  5. Mar 5, 2013 #4
    thank you! i figured that the velocity must have been an unknown constant (which would be ridiculous) or 0. I just wanted verification. Thank you for the fast reply guys!
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