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Homework Help: Elastic Collisions?

  1. Nov 19, 2013 #1
    1. The problem statement, all variables and given/known data
    A 25g object moving to the right at 20cm/s overtakes and collides elastically with a 10g object moving in the same direction at 15 cm/s. Find the velocity of each object after the collision

    2. Relevant equations

    3. The attempt at a solution
    First I tried to find one one of the v primes by using the momentum equation

    25(20)+10(15)=25v1'+10v2' and then simplifying it to

    Afterwards I plugged this in for v2' in v1+v1'=v2+v2' and solved through to get 2.57 cm/s for v1' which I know is incorrect. I know I did something wrong in the step above but I don't know how to approach this.
  2. jcsd
  3. Nov 19, 2013 #2


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    Homework Helper

    The red part is wrong.

  4. Nov 19, 2013 #3
    I'm not quite sure how to simplify that part it would help if you would tell me how :c
  5. Nov 19, 2013 #4


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    25v1'+10v2' is not 250(v1'+v2'). Isolate v2' from the equation 25v1'+10v2'=650, and plug in for v2' in v1+v1'=v2+v2'.

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