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

Perfectly elastic collisions (proof)

  1. Dec 16, 2004 #1
    An object collides elastically (perfectly) with another object (identical object) at rest. If it is not a head on collision how can i PROVE that the angle between them afterwards is 90 degrees? :confused: :bugeye:

    I have NO IDEA on what to do...it's been puzzling me and my friends for a little while now...

    help anyone?
  2. jcsd
  3. Dec 16, 2004 #2
    In a elastic collision momentum and KE are conserved:



    in this case the masses are the same so we can simplify:



    Consider now the first equation, look at the vectors [tex]\overrightarrow{v}_1_f[/tex] and [tex]\overrightarrow{v}_2_f[/tex], if they are added they are equal to [tex]\overrightarrow{v}_1_i[/tex], so you can picture the 3 of them as forming a triangle.

    If you picture this you can see that [tex]v^2_1_i=v^2_1_f+v^2_2_f[/tex] is the Theorem of Pythagoras. [tex]\overrightarrow{v}_1_i[/tex] is the hypotenuse so the other two sides form 90º.

    I hope the explanation is clear enough.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Perfectly elastic collisions (proof)