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!

Momentum of Bird on Swing after takeoff

  1. Jan 7, 2009 #1
    A 94 kg fullback moving east with a speed of 9.0 m/s is tackled by a 99 kg opponent running west at 3.0 m/s, and the collision is perfectly inelastic.

    (a) Calculate the velocity of the players just after the tackle.
    ___________________ m/s to the east
    (b) Calculate the decrease in kinetic energy during the collision.
    ___________________ J

    2. eqns
    conservation of energy/momentum
    Ke=1/2 * m * v^2

    3. The attempt at a solution
    a. 99*3=297

    I AM CLUELESS? I GOT 2695.6696
  2. jcsd
  3. Jan 7, 2009 #2


    User Avatar
    Homework Helper

    How did you get that number for part b?

    If the collision is perfectly inelastic, then the two objects stick together. Since you have the velocity after impact, you can get the kinetic energy after the impact.
  4. Jan 7, 2009 #3
    Last edited by a moderator: May 3, 2017
  5. Jan 7, 2009 #4
    what exactly should i do?
  6. Jan 8, 2009 #5


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You have not correctly calculated the initial kinetic energy of the the 2 players. Before the collision, each has its own mass, speed, and KE. KE is a scalar quantity. Just add them up. And your title is for the birds. :wink:
  7. Jan 8, 2009 #6


    User Avatar
    Homework Helper

    I don't follow your thinking for the collision. We can't talk, so we have to write very clearly. Does your teacher begin with a general statement for a collision problem such as:

    momentum before collision = momentum after collision

    This is most helpful and worth writing! You put the formulas on the next line (one mv for each moving object or stuck-together object), then the numbers on the next and finally the answer on the next line.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Momentum Bird Swing Date
Physics Word Problem. Yesterday at 10:55 PM
Momentum and Kinetic Energy Tuesday at 2:35 PM
Find x(t) for a car being pelted by rocks (1-D) Mar 9, 2018
Conservation of Angular Momentum of a bird Apr 20, 2015
Birds Colliding mid-air, Conservation of Momentum Oct 20, 2013