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: Question on waves where a rope attached to ceiling.

  1. Dec 4, 2012 #1

    ppy

    User Avatar

    1. The problem statement, all variables and given/known data
    A uniform rope of mass m and length L hangs from a ceiling. The mass of the rope below a point P is M.

    (a) Write down newtons second law for the segment of the rope of mass M and find the tension ata distance y above the lower end of the rope. Show that the speed of a transverse wave on the rope is a function of y, the distance from the lower end, and is given by v = sqr(gy).

    (b) Show that the time a transverse wave takes to travel the length of the rope is given by T = 2sqr(L/g)

    ***

    (a) v = sqr(tension/[mu]), where tension= Mg, and [mu] = M/y --- I think that's right.



    b) i do not have a clue for this bit am i meant to use speed= distance over time. If so the speed cant be the speed calculated in a) as then i do not get that answer.
    Thanks.



    3. The attempt at a solution
     
  2. jcsd
  3. Dec 4, 2012 #2

    haruspex

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    You have v = √(g/y). If x=x(t) is the distance of a wave crest from the bottom of the rope at time t, what differential equation can you write down for x?
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook