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# Confusion over a question watch

1. Here is the question and the answer

Question
A travelling wave has displacement given by:
y = 0.1 sin(!t − kx)

Sketch the initial profile between x = − and x = +; labelling the x
axis in units of .

Sketch should show a graph of y as a function of x with shape like -sin
(with y = 0 and decreasing at x = 0) covering 2 wavelengths moving between
y = ±0.1.

However surely it is to be drawn as a +sin wave as its 0.1sin and not -0.1sin?
2. (Original post by LowRider)
Here is the question and the answer

Question
A travelling wave has displacement given by:
y = 0.1 sin(!t − kx)

Sketch the initial profile between x = − and x = +; labelling the x
axis in units of .

Sketch should show a graph of y as a function of x with shape like -sin
(with y = 0 and decreasing at x = 0) covering 2 wavelengths moving between
y = ±0.1.

However surely it is to be drawn as a +sin wave as its 0.1sin and not -0.1sin?
I am trying to help but atm I cant read what some of it is ..could you edit it?
3. I didnt think the whole thing was needed but here it si

Question
A travelling wave has displacement given by:
y = 0.1 sin((lambda)t − kx)

Sketch the initial profile between x = −lambda and x = +lambda; labelling the x
axis in units of lambda.

Sketch should show a graph of y as a function of x with shape like -sin
(with y = 0 and decreasing at x = 0) covering 2 wavelengths moving between
y = ±0.1.
4. Look for the key points.

1) Initial profile => starting wave, i.e. t = 0. Therefore reduce equation to

y = 0.1 sin(-kx)

2) Use that k = 2Pi/lambda to get

y= 0.1sin(-2pi*x/lambda)

2) Now look for key points. Setting x = +lambda gives y = 0.1sin(-2*pi) = 0, so can now plot this point (x = lambda, y = 0)

Set x = -lambda, get 0 again (y = 0.1sin(2*pi) = 0)

For inbetween points set x = +-lambda/2 and see what happens...

Hope that helps!
5. It would look like this correct?

Sorry its messy

6. Thats almost it. Got the x intercepts right: zero at and and is max or min at and Only mistake is the whole thing is upside down - must have forgotten the minus sign in the sin expression!

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