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!

Homework Help: Help with conservation of energy

  1. Nov 8, 2007 #1
    1. The problem statement, all variables and given/known data
    Two billiard balls move of equal mass move at right angles and meet at the origin of an xy coorindate system. Ball A is moving upward along the y axis at 2.0m/s and ball B is moving to the right along the x axis with a speed of 3.7m/s. After the collision, assumed elastic, ball B is moving along the positive y axis . What is the final direction of Ball A and what is their speeds.

    2. Relevant equations
    Conservation of momentum :

    I know that the masses cancel as they are the same.
    But that still leaves me with 2 unknowns in that equation. Do I have to use trig functions to fing the velociy of ball B and then use the momentum to find velocity of ball A?? but then how do i find the direction of ball A

    3. The attempt at a solution
  2. jcsd
  3. Nov 8, 2007 #2
    In an elastic collision linear momentum and energy are conserved. You have two independent lines (x and y) so that gives you three equations ...
  4. Nov 8, 2007 #3
    O right sorry I forgot to write out the equation for the momentum along y. so in the x equation for example Vax= 0 and simiarly for the y equation? and is the third equation the kinetic energy one?? But I am sill confused as too how i find the direction of the A Ball.
  5. Nov 8, 2007 #4
    Don't worry about finding the direction of the A ball; if you find its velocity in the x direction and its velocity in the y direction ...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook