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

Homework Help: Basic Physics question (2-d momentum)

  1. Apr 21, 2005 #1
    I can NOT figure this question out, it's the only one I havent gotten, can someone help?

    The drawing shows a collision between two pucks on an air-hockey table. Puck A has a mass of 0.020 kg and is moving along the x axis with a velocity of +5.5 m/s. It makes a collision with puck B, which has a mass of 0.040 kg and is initially at rest. The collision is not head-on. After the collision, the two pucks fly apart with the angles shown in the drawing.


    (a) Find the final speed of puck A.
    ______ m/s
    (b) Find the final speed of puck B.
    ______ m/s
  2. jcsd
  3. Apr 21, 2005 #2
    Hi atlbraves,

    usually you must propose a solution or give some hints ........but today I'll make an exception for you:

    You must write the the conservation law for angular momentum:


    Then you have to write the above vectorial equation on Ox (the direction of the initial velocity of A) and Oy (perpendicular on it):

    Ox: [tex]p_{A0}=p_A \cdot cos(\alpha_A)+p_B \cdot cos(\alpha_B)[/tex]
    Oy: [tex]p_A \cdot sin(\alpha_A)-p_B \cdot sin(\alpha_B)=0[/tex]
  4. Apr 21, 2005 #3
    thanks, i figured it out, i actually ended up knowing how to do it, the reason i wasnt getting the answer correct is i messed up a calculation, thanks for the help anyways
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook