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: Speeds of tennis balls after collision

  1. Feb 3, 2010 #1
    1. The problem statement, all variables and given/known data

    A 0.0600 kg tennis ball, moving with a speed of 2.50 m/s, has a head-on collision with a 0.0900 kg ball initially moving away from it at a speed of 1.00 m/s. Assuming a perfectly elastic collision, what is the speed and direction of each ball after the collision?

    2. Relevant equations

    m1v1+m2v2 = m1v1'+m2v2'

    3. The attempt at a solution

    with the given, I know that
    m1= .06 kg
    m2=.09 kg
    v1= 2.5 m/s
    v2= 1.0 m/s
    after this, I don't know where to start?
  2. jcsd
  3. Feb 3, 2010 #2
    Hi balletgirl

    Plug all the data to the equation you wrote and you lack one more equation, which is V1-V2=V2' - V1'
  4. Feb 3, 2010 #3
    Okay so I do 2.5-1.0= V2'-V1'. I don't understand how you find those final numbers.
    .06kg(2.5m/s) + (.09kg)(1.0m/s) = m1v1'+m2v2'
  5. Feb 3, 2010 #4
    You have two equations and two variables so just use elimination or substitution
  6. Feb 3, 2010 #5
    I don't understand the concept.
    I thought I was solving for four variables: m1' v1' m2' and v2'
    Anyways I got to .135=m1v1'+m2v2'
    1.5= V2'-V1'

    it didn't work out when I tried using elimination or substitution
  7. Feb 3, 2010 #6
    Okay just realized a dumb mistake. The mass will stay the same. This will make everything a lot easier for me.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook