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Homework Help: A 3.0 g coin moving to the right at 26.0 cm/s makes an elastic head-on colli

  1. Dec 11, 2007 #1
    1. The problem statement, all variables and given/known data

    A 3.0 g coin moving to the right at 26.0 cm/s makes an elastic head-on collision with a 12.0 g coin that is initially at rest. After the collision, the 3.0 g coin moves to the left at 12.5 cm/s.
    (a) Find the final velocity of the other coin.
    _____cm/s to the right
    (b) Find the amount of kinetic energy transferred to the 12.0 g coin.

    2. Relevant equations

    for part a, i know you have to do conversions to get to M and Kg.
    for part b, .5mv^2

    3. The attempt at a solution

    i know that KE of the 2nd coin = (m of second coin)(.5)(Velocity of second coin ^2)

    but i'm STUCK on part A!!!!
  2. jcsd
  3. Dec 11, 2007 #2
    Use conservation of momentum:


  4. Dec 13, 2007 #3
    i found part A, and it's 9.6cm to the right.
    but now i am stuck on part B.
    no matter what i do, it's not working!

    .....i tried this:
    KE of second coin=(Mass of second coin).5(Velocity of 2nd coin^2)
    so it'd look like:
    BUT since it's 9.6 CM/s, to convert it to m/s it would be .096
    which is: .00055296

    why is it wrong!?
    Last edited: Dec 13, 2007
  5. Dec 13, 2007 #4
    What's the answer given in the book? Btw, 12.0 g is 0.012 kg.
  6. Dec 13, 2007 #5


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    Science Advisor

    I'll unmark this as solved since you still seem to be asking questions on it.
  7. Dec 13, 2007 #6
    ok i think this is how u do it
    first u need to find kinetic energy before contact and find the kinetic energy of the coin A
    and u subtract the original kinetic to the kinetic of coin A u will get the kinetic of coin B
    (assumed that the moving coin is A and the resting coin is B)
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