# Homework Help: Sketching waves at a boundary

1. Nov 8, 2015

### Nicknacks

Hi, so I have this question:

A wave pulse on a string has the dimensions shown in the figure (Figure 1) at t = 0. The wave speed is 40 cm/s.
a) Draw the total wave on the string at t=15ms, 20ms 25ms, 30ms, 35ms, 40ms and 45ms. b) repeat part (a) for the case in which the end of the string is free to slide along a pole.
I can do part a for 15ms and 20ms but not sure about the rest.

http://oi55.tinypic.com/25khmc0.jpg

I get that i need to for example:
400mm/s * 25*10^-3 = 10

so the graph moves towards the left by 10mm but the end point can only move 8mm before it reaches the fixed point so how would i draw it?

Also how would i do part b?

The graph is show below

Thanx:)

Last edited by a moderator: May 7, 2017
2. Nov 8, 2015

### haruspex

One way to think about wave reflections is to regard the fixed end as superimposing a wave of the same speed, amplitude and frequency in the opposite direction. The phase is such that the sum of the two waves at that end point is always zero.
Does that help?

3. Nov 9, 2015

Yes, thanks.