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!

Momentum, Energy

  1. May 16, 2010 #1
    1. The problem statement, all variables and given/known data
    Two particles of masses m and 3m are connected by a light rigid rod. The system rests on a smooth horizontal table, the heavier mass due east of the lighter mass. The heavier mass is projected with initial velocity uj. Find the velocities of the particles when the rod runs north-south.


    2. Relevant equations
    Conservation of momentum, conservation of energy.


    3. The attempt at a solution
    Applying conservation of momentum in the j direction, 3m(u) + m(0) = 3mv + mw.
    3u = 3v + w.

    Conservation of energy, 1/2(3m)u2 = 3mgh +1/2(3m)v2
    u2 = 2gh + v2

    I've no idea where to go from here.
    This isn't homework, just a question I came across while revising for exams.
     
    Last edited: May 17, 2010
  2. jcsd
  3. May 16, 2010 #2

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Hi Maybe_Memorie! :smile:

    (try using the X2 tag just above the Reply box :wink:)
    erm :redface: … leave out the mgh ! :biggrin:
     
  4. May 17, 2010 #3
    Why? The 3m mass gains vertical height.
     
  5. May 17, 2010 #4

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    No …
    … everything's horizontal.
     
  6. May 17, 2010 #5
    The 3m mass is projected with a velocity uj, i.e. a velocity of u in the j-> direction, upwards.
     
  7. May 17, 2010 #6

    tiny-tim

    User Avatar
    Science Advisor
    Homework Helper

    Where I live, that's the k direction. :wink:

    Anyway, if the rod starts east-west, and ends up north-south (as in the question), how can it ever move upwards??
     
  8. May 18, 2010 #7
    It's like the large mass moves in a circle around the small mass. So the 3m mass gains height in rotating.

    It may be possible to treat it as a compound pendulum.
     
  9. May 18, 2010 #8
    Any suggestions?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Momentum, Energy
  1. Energy? or momentum? (Replies: 1)

  2. Energy momentum (Replies: 1)

  3. Momentum + Energy (Replies: 8)

  4. Energy and momentum (Replies: 0)

  5. Energy and momentum. (Replies: 7)

Loading...