1. Not finding help here? Sign up for a free 30min 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!

Elastic Collision with a Spring Constant

  1. Aug 5, 2012 #1
    1. The problem statement, all variables and given/known data

    A pinball with mass 80g is struck by a lever with mass 80g in a pinball machine in an elastic collision. The lever was pulled back 2 cm by a spring with spring constant k=1.4N/cm. What is the speed of the ball just after collision?

    2. Relevant equations
    F=kx

    1/2kx^2=1/2mv^2

    M1V1 = M2V2



    3. The attempt at a solution

    1/2 (2.8)(4)=5.6 5.6=1/2 (80) v^2 <-- trying to find velocity of lever just before contact

    5.6/40 = v^2 V=.37

    now this is where i get even more stuck, the masses of the ball and the lever are equal and they cancel out in the equation M1V1 = M2V2, which would leave the velocities as being equal. However, the answer choices are as follows:

    A) 1.1 m/s
    B) 1.4 m/s
    C) 11 m/s
    D) 14 m/s

    If someone can shed some light on how to solve this problem it would be greatly appreciated.
     
  2. jcsd
  3. Aug 5, 2012 #2
    First thing I would look at is units. g to kg

    centimeters to meters, I would change both and see how it works out.
     
  4. Aug 7, 2012 #3
    i tried that, and i am still stumped
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook