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: Need help on Collision problem

  1. Nov 9, 2004 #1
    After a completely inelastic collision, two objects of the same mass and initial speed are found to move away together at 1/2 their initial speed. Find the angle between the initial velocities of the objects.

    Solution is here http://www.physics.sfsu.edu/~senglish/APphysicswebsite/collisions/solutions%20on%20collisions/17.pdf [Broken]

    My first atempt to solve this problem was drawing my diagram so that both objects converge towards the positive y-axis instead of the positive x-axis as seen in solution.

    v=initial velocity vf= final velocity
    so the x-comp mv cos A - mv cos B= 0
    y-comp mv sin A + mv sin A = 2m vf

    Well it didn't work, so i gave up and redrew my diagram like the one in the solution and solved it that way. I'm starting to conclude that my original idea solved for a different angle for the problem.

    What did i do wrong in solving the problem with my original diagram with the objects converging towards the positive y-axis
    Last edited by a moderator: May 1, 2017
  2. jcsd
  3. Nov 9, 2004 #2
    The x component momentum is

    mv cosA - mv cosB = 0


    mv cosA - mv sinA
  4. Nov 9, 2004 #3
    typo :mad:

    anyway your right

    my calculations so far
    x-comp mv cos A - mv cos B= 0 A=b but then its 0=0 which doesn;t really help

    so looking at the y-comp
    y-comp mv sin A + mv sin A = 2m vf

    2mv sinA = 2mv 1/2v

    sin A = 1/2
    A= 30 degrees x2 60 degrees

    The answer is suppose to be 120 degrees, but then my answer plus the actual is 180 degrees. Therefore i think the angle i solved for was the outside angle, but why :confused:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook