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: Elastic collisons in space

  1. Oct 31, 2009 #1
    Two balls Y and Z collide elastically in space. If Z is initially at rest how would you choose it's mass in relation to Y so that it would recoil with the greatest (1) KE (2) Momentum

    Kinetic Energy: KE = (1/2)mv^2

    Momentum: P = mv

    Would you have to have a smaller mass for Z so that it would recoil with greater KE than Y?

    And for momentum would you have to have a larger mass for Z so it would recoil with greatre momentum?

    How do you explain them in terms of the equations? I think I understand the momentum....if you plug in larger mass than you have a larger P...but KE I'm not sure? Wouldn't you also have a larger KE if you plugged in larger mass? If Z was really large it wouldn't move it all so I would think it would have to be small would it not?
  2. jcsd
  3. Nov 3, 2009 #2
    Anyone have input for this?
  4. Nov 3, 2009 #3
    Momentum is always conserved for all cases so the ball or block that is going to hit the one that is resting has a constant value of momentum;

    as you can see from the equaiton p=m.v the value of the momentum is about the values of the blocks or balls mass and velocity.

    So to get the max value of kinetic energy i would take m as a small value because the degree of it is 1, if you double your velocity your kinetic energy would increase as a factor of 4.

    (Kinetic energy of a block is 1/2mv2 as you mentioned )
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook