1. Not finding help here? Sign up for a free 30min 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!

Head on elastic collision

  1. Oct 27, 2012 #1
    1. The problem statement, all variables and given/known data
    A 2.0 kg ball is traveling east at 8.0 m/s when it has a perfectly elastic head-on collision with a 3.0 kg ball traveling west at 10.0 m/s. What are the final velocities of the two balls?


    2. Relevant equations

    http://www.nvcc.edu/home/tstantcheva/231files/G09_hw.pdf [Broken]
     
    I used the derived equation from page 4.

    3. The attempt at a solution
    For the 2.0 kg ball I got -13.6 m/s.
    For the 3.0 kg ball I got -15.6 m/s.
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Oct 27, 2012 #2
    Please show your work. The new speeds for both balls are faster than either initial speed. Elastic collisions conserve energy. Your speeds indicate energy was somehow created.
     
  4. Oct 27, 2012 #3
    vf1 = ((m1)(v1) + m2((2*v2) - v1)) / m1 + m2
    vf1 = (16 + 3(-20 - 8))/5
    vf1 = -13.6 m/s

    vf2 = v1 + vf1 - v2
    vf2 = 8 + -13.6 - 10
    vf2= -15.6 m/s

    I'm assuming my problem is from setting the values of the speeds in the opposite direction to negative, but I thought this must be done?
     
  5. Oct 27, 2012 #4
    You have a sign error for the second velocity. What is -v2?
     
  6. Oct 27, 2012 #5
    Ah I see what I did wrong, v2 = 4.4 , and v1 = -13.6, substituting them into the conservation of momentum equation yields 14 = 14.
     
  7. Oct 27, 2012 #6
    You are right. Since you're checking momentum, you should also check energy as well. There are two conservation theorems to satisfy.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Head on elastic collision
Loading...