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!

Slider energy on rod

  1. Feb 19, 2007 #1
    1. The problem statement, all variables and given/known data
    Collar B has a mass of 4 kg and is attached to a spring of constant 1500 N/m and of undeformed length 0.4 m. The system is set in motion with r = 0.2 m, v_theta = 6 m/s, and v_r = 0. Neglecting the mass of the rod and the effect of friction, determine the radial and transverse components of the velocity of the collar when r = 0.5 m.


    2. Relevant theories

    Conservation of energy - kinetic and potential energy

    3. The attempt at a solution

    I used conservation of energy :

    V_spring_initial = V_spring_final + T_slider_final

    x_initial_spring = abs(0.2-0.4)
    x_final_spring = abs(0.5-0.4)


    I solved for v_r and got 3.35 m/s, which is NOT the right answer.

    If I figure out how to solve for v_r, I'm still in the situation where I don't really know how to solve for v_theta. I'm thinking I can determine the force due to the spring and set that equal to m*a_normal, solve for v_theta there (because v^2 = (v_tangential)^2 = (v_theta)^2).

    Can I get some help? Thanks a bunch!
     

    Attached Files:

  2. jcsd
  3. Feb 19, 2007 #2
    Use conservation of angular momentum to find the velocity in the tangential direction as a function of the radius.

    Use a net force equation to find the velocity in the radial direction as a function of the radius. (You can consider it as an "inertial" frame with a fictional force, if you want.)
     
  4. Feb 19, 2007 #3
    We haven't done angular momentum in class yet. While I do know it, he wants us to try and stick to the concepts we know.
     
  5. Feb 20, 2007 #4
    Is there any more thoughts on this one or no??
     
  6. Feb 20, 2007 #5

    andrevdh

    User Avatar
    Homework Helper

    If one looks at just the SHM motion of the slider its energy stays constant throughout the motion:

    [tex]\frac{1}{2}Ax^2[/tex]

    which enables one to calculate the radial velocity at any position.

    Looking at the bigger picture the total mechanical energy (which will stay
    constant since the slider is subject to a conservative force) of the slider should also include its rotational kinetic energy:

    [tex]\frac{1}{2}I\omega ^2[/tex]

    , where its rotational velocity is determined by the tangential velocity.
     
    Last edited: Feb 20, 2007
  7. Feb 20, 2007 #6
    But the concept of moment of inertia hasn't been formally introduced in our class yet, so we can't really use that equation.
     
  8. Feb 20, 2007 #7
    How did you get the answer for Vr? What principle did you use? I was going to suggest you use the work-energy principle.
     
  9. Feb 21, 2007 #8

    andrevdh

    User Avatar
    Homework Helper

    Ok. You can then still use the fact that T + V will stay constant. The speed that you get will be the real speed of the slider, that is the tangential and radial speed combined or just v.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Slider energy on rod
  1. Slider on rod (Replies: 2)

  2. Induction slider (Replies: 12)

Loading...