Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Collisions problem (How should I approach it)

  1. Dec 13, 2003 #1
    Hi all,

    I came across a problem on collisions on one of my professors old exams. The problem is:


    The way I am trying to approach it is by applying the conservation of linear momentum and energy, but the problem is that I still get left with 3 unknowns.

    Here is what I know:
    Before the collision, only block A has kinetic energy.

    After the collision, the K.E. of system is (1/2 K.E. initial). block A has -1/2MV^2 and block B has 1/2MV^2.

    The final collision is what confuses me. Should I just work with K.E.i (only block A moving) with conservation of linear momentum?

    Any help would be greatly appreciated. Thanks!
    Last edited by a moderator: Apr 20, 2017
  2. jcsd
  3. Dec 13, 2003 #2
    by cons of p,
    where v_2f is reckoned as negative
    By the energy conditions,
    [tex]m_1v_{1i}^2=\frac {1}{2}(m_1v_{1f}^2+m_2v_{2f}^2)[/tex]
    which gives two equations with two unknowns.
  4. Dec 13, 2003 #3
    Thanks for the reply
    StephenPrivitera. I am just wondering why you made m_2v_2f negative in the first equation?? Should it be the other way around?
  5. Dec 14, 2003 #4

    Doc Al

    User Avatar

    Staff: Mentor

    The equations should be:
    [tex]\frac {1}{4}m_1v_{1i}^2=\frac {1}{2}(m_1v_{1f}^2+m_2v_{2f}^2)[/tex]
    (where the speeds are all positive)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook