Displacement of a wave

1. Apr 21, 2014

BOAS

Hi,

I don't understand why I keep getting a negative result...

1. The problem statement, all variables and given/known data

The displacement (in metres) of a wave is given according to

y = 0.26 sin(πt − 3.7πx),

where t is in seconds and x is in metres,

What is the displacement y when t = 38 and x = 13 [m] ?

2. Relevant equations

3. The attempt at a solution

The wave travels in the +x direction because as time increases so does the displacement, so i'm expecting a +ve result.

$y = 0.26 \sin (\pi 38 - 3.7 \pi 13)$

This keeps giving me $y = -0.1367$ as an answer which surely can't be correct.

I don't know what i'm doing wrong...

Thanks,

BOAS

2. Apr 21, 2014

HallsofIvy

Staff Emeritus
You seem to be misunderstanding the word "displacement". A wave moves up and down as it travels. It is, as you have calculated, the y coordinate, not movement in the x direction. It certainly can be negative.

3. Apr 21, 2014

BOAS

You're right, I had misunderstood that - Thanks, it makes more sense now.

I also did the calculation in degrees which explains why the magnitude of my answer was wrong.