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: Two pendulums banging into each other problem.

  1. Aug 20, 2013 #1
    1. The problem statement, all variables and given/known data

    A system contains two metal balls hanging from strings of length !.0 m. Pendulum A has a mass of 2.0 kg and B has a period of 2.0s. They are released from the same height at the same time and collide right in the middle of their arcs. If pendulum A comes to a complete stop while B moves backwords with half of its original speed, what is the mass of pendulum B?

    2. Relevant equations

    Conservation of momentum.


    3. The attempt at a solution

    My first thought was the conservation of momentum. 2Va+MbVb=-(1/2)MbVb. Of course theres 3 variables so i couldnt solve it but then i thought that since the balls were colliding in the middle of their arcs that maybe they're velocities were the same. So Va=Vb. From that logic I get that the mass of B is -4/3 which obviously makes no sense..... Im not sure what im doing wrong. Im gratful for any help. Thanks in advance
     
  2. jcsd
  3. Aug 20, 2013 #2

    ehild

    User Avatar
    Homework Helper


    The momentum is a vector. The balls move in opposite directions just before they collide. Va is not equal to Vb.


    ehild
     
  4. Aug 21, 2013 #3
    Use the equation for the period of a pendulum to help you find Vb.
     
  5. Aug 21, 2013 #4

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    The time taken is irrelevant. You cannot deduce any actual velocity since you do not know the original height. ehild's hint is the way forward.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Loading...