1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    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!

Elastic collision between two bodies

  1. Apr 13, 2014 #1
    1. The problem statement, all variables and given/known data
    A body of mass 2.0Kg makes an elastic collision with another body at rest and continues to move in the original direction but with one-fourth of its original speed. What is the mass of the other body?

    2. Relevant equations
    Because it is an elastic collision I know that Energy and momentum are conserved.

    So, m1v1i+ m2v2i = m1v1f+m2v2f

    V1f = V2f = Vf

    3. The attempt at a solution

    I'm not really sure where to go because I'm not given the velocity of the second block after the collision.

    2*v1i + 0 = 2*(1/4v1i) + m2v2

    I'm confused because it states that the original block continues to move in the original direction. Because the blocks don't adhere to each-other or go in opposite directions I'm not sure what to do.
    Last edited: Apr 13, 2014
  2. jcsd
  3. Apr 13, 2014 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Lets say block A is the 2kg one initially moving and block B is the one initially stationary.
    You are not told that the blocks do not stick together.
    Even if they do not, it is possible for block B to end up moving faster than block A.

    You are not told the mass of block B or it's final velocity, but you can write down two equations which must be true simultaneously. Write them down.
  4. Apr 14, 2014 #3

    Just so you know you're told that it's an perfectly elastic collision so you know that both momentum and kinetic energy is conserved.

    So why not just isolate for a variable in one equation plug it into the next equation to get the answer, while cancelling out any unknowns
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted