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: Standing Waves

  1. Apr 6, 2004 #1

    new324

    User Avatar

    Once, again I find myself in need of a little help. Any hints/tips would be well appreciated.
    In the arrangement shown in (attachment), a mass m can be hund from a string (with a linear mass density of .002 kg/m) that passes over an ideal pulley. A string with a length of L=2 meters is connected to a vibrator of constant frequency, Find the mass m of the object when the standing waves with a fundamental frequency of 20 Hz are observed in the string.

    Update: Alright I substitued a few equations and have determined the Tension. My assumption is that the mg is going to be half of the tension (half is mg the other half is the wave). Is this assumption correct? If not, any hints?
     

    Attached Files:

    Last edited: Apr 6, 2004
    new324, Apr 6, 2004
  2. jcsd
    Phys.org - latest science and technology news stories on Phys.org
  3. Apr 6, 2004 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Think about it: The tension in the string must support the weight of the mass. Right?
     
    Doc Al, Apr 6, 2004
  4. Apr 6, 2004 #3

    kuengb

    User Avatar

    No, it's tension=m*g. Look at the situation without a wave: At the end of the string you'll have to pull with a force of m*g to prevent the mass from falling; hence the tension in the whole spring is m*g. If you run the oscillator now (with an arbitrarily small amplitude), this won't change, force can't be "splitted up" into two halfs in the same string.

    Bruno
     
    kuengb, Apr 6, 2004
  5. Apr 6, 2004 #4

    new324

    User Avatar

    Awesome. You guys are such a huge help to me. I always try and make things tougher than they are. Thank You!
     
    new324, Apr 6, 2004
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook