# Homework Help: Standing wave concept problem.

1. Sep 17, 2009

### Eric_meyers

1. The problem statement, all variables and given/known data
"A standing wave in the form of a string attached to a driven tuning fork is created. We then move the furthest boundary point to a node somewhere along the string. The node of course was originally at rest by definition. The string behind the node with the boundary point ceases to oscillate. Why?

2. Relevant equations

3. The attempt at a solution

So in this problem I was thinking of Newton's law of equal and yet opposite force, but the node was already at rest so with no motion I couldn't utilize this concept. I'm drawn between using some concept of energy, that the boundary point is creating a point of discontinuity in the medium so the wave can't propagate beyond it... but I'm not sure exactly how it creates this point of discontinuity.

Is it absorbing the energy? How? I'm drawing a big blank because I don't see the boundary point doing work on the string since the net displacement is 0.

2. Sep 17, 2009

### turin

I'm pretty sure that the boundary point does no work on the string; as you say.

This is a good question. I don't know what the answer is "supposed to be", but I'm guessing that they want you to decompose the standing wave into travelling waves, and then consider the effect of the boundary condition on the travelling waves.