More questions like this waves in water problem?

Question with diagram: https://postimg.cc/yDfXFZqd

For some reason this question has been itching me for weeks whilst revising for the ENGAA and I finally was able to get the correct answer in a way I can understand. Ive been through every engaa question on Waves in section 1 and 2 and was wondering if anyone has managed to solve this/ found anymore problems similar (I.e: Involving water waves)??

I'm currently using Isaac physics and am re-doing some previous Oxford PAT questions to find something like it

Reply 1

username6303304

I managed to solve this one fairly quickly by equating 1/0.8 to (1.5 + L)/L and solving, where L is the wavelength. If you want me to explain I can but considering you solved it I assume that you probably get it.
I think that there's a relatively similar one in one of the papers, I saw it the other day I'll see if I can find it
Try question 13 from Engaa 2022, section 1a and maybe 18 from engaa 2017 section 1a. They aren't exactly the same but they have the same sort of process where you have to consider the time period etc. :smile:

Hope that helps

(edited 7 months ago)

Reply 2

MonoAno555

Original post by bxnh

Hope that helps

Hi again thanks for the advice (your method for the question I posted was better). Just tried Engaa 2022 section 1A Q14 (the one on waves) and using a similar technique to the one I originally posted (by using the X distance as a fraction of the wavelength). Just want to ask if you got something similar:

4m = 2λ, so λ = 2m,
X =(1/4)λ (from the graph) at t=0,
So at t=7, X2 = (7/4)λ = (1/4)λ + (3/2)λ,

So as Wave speed is constant: (1/4)λ / 0 = (1/4)λ + (3/2)λ / 0+7, which has no solutions.

Has is why the answer is 0mm = C?

(edited 6 months ago)

Reply 3

Eimmanuel

Study Forum Helper

Original post by MonoAno555

Hi again thanks for the advice. Just tried Engaa 2022 section 1A Q14 (the one on waves) and using a similar technique to the one I originally posted (by using the X distance as a fraction of the wavelength). Just want to ask if you got something similar:

4m = 2λ, so λ = 2m,
X =(1/4)λ (from the graph) at t=0,
So at t=7, X2 = (7/4)λ = (1/4)λ + (3/2)λ,

So as Wave speed is constant: (1/4)λ / 0 = (1/4)λ + (3/2)λ / 0+7, which has no solutions.

Has is why the answer is 0mm = C?

I assume that you are “speaking” the question in the picture above as the question number does not match your description in the quote.

There are 2 ways of “seeing” the solution.
First way, visualise how the particle has moved for 7.0 ms.
We know that the period is 4.0 ms.
At t = 4.0 ms, the particle has returned to position X.
At t = 5.0 ms, the particle has moved to the rest or equilibrium position as indicated by the green downward arrow.
At t = 6.0 ms, the particle has moved from the rest position to the trough as indicated by the blue downward arrow.
At t = 7.0 ms, the particle has moved from the trough back to the rest position as indicated by the red upward arrow.

The second way is visualising where the disturbance has moved from X in 7.0 ms along the wave.
At t = 4.0 ms, the disturbance has travelled to the next crest as indicated by the purple horizontal arrow.
In the next 3.0 ms (t = 7.0 ms), the disturbance has travelled 0.75λ (3.0/T, T is period) as indicated by the red horizontal arrow. The disturbance is at the equilibrium position.