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!

Springs and friction and energy, etc.

  1. Oct 23, 2007 #1
    1. The problem statement, all variables and given/known data
    A small block of mass m is pressed up
    against a spring. The spring has constant k
    and is compressed a distance x. The block
    slides along a track up and around a loop
    of radius r and down and out on the far
    side, as shown. At the top of the loop, the
    loop exerts a normal force on the block
    equal to the weight of the block. Neglect

    Determine the compression distance, x, in terms of given quantities k, m, r and g.

    2. Relevant equations

    U[tex]_{spring}[/tex] = 1/2kx[tex]^{2}[/tex]
    KE = 1/2mv[tex]^{2}[/tex]
    U[tex]_{grav}[/tex] = mgh

    3. The attempt at a solution

    I started with energy conservation, but im not sure if you just set U[tex]_{spring}[/tex] equal to the sum of KE and U[tex]_{grav}[/tex]

    The picture of the problem can be seen here: http://img137.imageshack.us/img137/7804/41935428tm6.th.jpg [Broken]
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Oct 23, 2007 #2
    I'm not sure if I understood the problem. Why is the problem called Springs and FRICTION and energy?

    However, I would start with the loop:

    You know that in the look, the gravitational potential is equal to the energy of the block. Therefore:

    [tex]E_{kin}+m\cdot g\cdot h\cdot= U_{grav}[/tex]

    where h is equal to two times the radius r.

    Now, you can set up another equation because you know that the energy of the block at the beginning was zero (no kinetic energy and no gravitational energy):

    [tex] E_{kin}= 1/2\cdot k\cdot x^{2}[/tex]

    Now, you should know how to solve the problem...
  4. Oct 23, 2007 #3
    mistake on title

    yea sorry about the title, it wouldnt let me edit it though. :tongue2:

    thanks for the help!
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook