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!

Kinetic Energy Ping Pong ball Question

  1. Jun 4, 2008 #1
    [SOLVED] Kinetic Energy Question

    1. The problem statement, all variables and given/known data
    A 7.0 kg bowling ball moves at 2.35 m/s. How fast must a 2.40 g Ping-Pong ball move so that the two balls have the same kinetic energy?

    m1= 7.0kg
    v1= 2.35m/s
    m2= .0024kg

    2. Relevant equations

    I know that:
    KE= 1/2mv^2

    3. The attempt at a solution
    I set my equation like so:

    and I reduced it to this:

    I plugged in the values and solved for v2:
    (7.0kg)(2.35m/s)=v2 (.0024kg)
    v2= 6854.17

    I put this answer in and it tells me...
    wrong check mark
    Your answer differs from the correct answer by orders of magnitude. m/s

    What am I doing wrong? Please point me in the right direction.
    Last edited: Jun 4, 2008
  2. jcsd
  3. Jun 4, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor



    You made an error here. The kinetic energy equation doesn't reduce to this.

    (Don't leave off squaring the speeds.)
  4. Jun 4, 2008 #3
    Thank you Doc Al.

    The correct answer was 127m/s
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook