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: Two dimensional momentum

  1. Dec 25, 2003 #1
    I have a problem with this question,

    1. Two rolling golf balls of the same mass collide. The velocity of one ball is initially 2 m/s [E] After the collision, the velocities of the balls are 2.49 m/s [62.8° North of West] and 2.37 m/s [69.2° South Of East]. What are the magnitude and direction of the unknown velocity?

    Basicall I did:

    For x component:

    V1 + V2 = V1'cos(180°-62.8°) + V2'cos(360°-69.2°)

    I solved for V2

    I did the same for the y component then I took the x and y component values and did the pythagoras theorem to get the angle and value...The value at the back of the book is 3 m/s and moving W for the initial velocity of the other ball...My answer was 4.7 m/s [20° South of West]

    Whats my mistake?
  2. jcsd
  3. Dec 26, 2003 #2


    User Avatar
    Science Advisor
    Homework Helper

    You certainly have the right idea. If you show more work I might be able to tell you where the problem is.
  4. Dec 26, 2003 #3
    I've got two answers and one of them is at the back of book. How do I know which ball moves where?
  5. Dec 26, 2003 #4


    User Avatar
    Science Advisor

    Are you assuming conservation of energy (perfectly elastic collision)? If so you can use V12+ V22= V1'2+ V2'2.
  6. Dec 26, 2003 #5


    User Avatar
    Science Advisor
    Homework Helper

    It's not necessary here.
    He's got two unknowns, and two equations from conservation of momentum. The only unknowns are the x and y components of one ball's inital velocity, and the other inital and both of the final velocities are given.
  7. Dec 26, 2003 #6
    Im assuming its a perfectly elastic collision since its two golf balls
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook