1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Elastic Collision and speed of a ball

  1. Nov 20, 2009 #1
    1. The problem statement, all variables and given/known data

    A 120 g ball moving to the right at 4.5 m/s catches up and collides with a 420 g ball that is moving to the right at 1.2 m/s.

    If the collision is perfectly elastic, what is the speed of the 420 g ball after the collision?

    2. Relevant equations

    [tex]m_1v_{1i}+}m_2v_{2i} = m_1v_{1f}+m_2v_{2f} [/tex]

    3. The attempt at a solution

    I manipulated the formula a little bit to solve for V2_f and came up with this:
    [tex](m_1v_{1i}+}m_2v_{2i} - m_1v_{1f}) / m_2[/tex]

    then I plugged in my numbers:
    (.12*4.5 + .42*1.2 - .12*.63) / .42

    simplified to this:
    (.54 + .504 - .0756) / .42

    and got 2.3057. Mastering physics said that is wrong however and I'm not sure what I'm doing wrong. Is the conservation of momentum the correct equation for this problem? I found the velocity of the 120 gram ball fine, which was .63 m/s, but am stuck on this one. Any help would be appreciated.
     
  2. jcsd
  3. Nov 20, 2009 #2

    rl.bhat

    User Avatar
    Homework Helper

    Hi Atlos, welcome to PF.
    How did you get v1f = 0.63 m/s?
     
  4. Nov 20, 2009 #3
    I came to find v1f by using the following equation:

    [tex][(m_1-m_2) / (m_1+m_2) ]v_{1i} + [2m_2 / (m_1+m_2]v_{2i}[/tex]
     
  5. Nov 21, 2009 #4
    A useful fact for straight line elastic collision is that

    v_2b - v_1b = - (v_2a - v_1a)

    v_1a = velocity of m1 before collision
    v_1b = velocity of m1 after collision etc.

    Relative velocity before the collision is the same as after, just opposite in sign.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Elastic Collision and speed of a ball
Loading...