Displacement of a wave

  • Thread starter BOAS
  • Start date
  • #1
555
19
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.

[itex]y = 0.26 \sin (\pi 38 - 3.7 \pi 13)[/itex]

This keeps giving me [itex] y = -0.1367[/itex] as an answer which surely can't be correct.

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

Thanks,

BOAS
 

Answers and Replies

  • #2
HallsofIvy
Science Advisor
Homework Helper
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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
555
19
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.
 

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