Displacement of a wave: Understanding Negative Results

[BOAS]

Hi,

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

Homework Statement

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] ?

Homework Equations

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

 

[HallsofIvy]

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.

 

[BOAS]

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.

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.