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# January 2012 Waves - Confused? watch

1. http://store.aqa.org.uk/qual/gce/pdf...2-QP-JAN12.PDF

Question 7B.

Mark Scheme:

(vertically) downwards (1⁄4 cycle to maximum negative displacement) then upwards (1⁄4 cycle to equilibrium position and 1⁄4 cycle to maximum
positive displacement)
down (1⁄4 cycle) to equilibrium position/zero displacement and correct reference to either maximum positive or negative displacement or correct reference to fractions of the cycle
candidate who correctly describes the motion of a knot 180 degrees out of phase with the one shown can gain maximum two marks (ie knot initially moving upwards)
Why does is say vertically downwards first. I was thinking it would go up first then down...
2. You may be thinking of the knot moving to the right. It is fixed and can only move up or down vertically. Not left or right.
As such it has to move with the up and down motion of the rope at that point.
If the knot was a cork floating on the surface of a pond and a water wave was approaching from the left as shown, which way would the cork move?
The next part of the wave to reach the cork or knot is below the mean level. Not above.
3. It says the wave is a progressive wave so the knot would not be stationary and would move right or left...

I think the knot would move right and up after a quarter cycle...
4. (Original post by Math12345)
It says the wave is a progressive wave so the knot would not be stationary and would move right or left...

I think the knot would move right and up after a quarter cycle...
Progressive just means it's not a stationary/standing wave.

The rope particles are just going up and down, there will be no 'surfboarding' in the direction the wave is moving. You can't move the molecules in the rope further away by sending a wave along it.
5. (Original post by Math12345)
It says the wave is a progressive wave so the knot would not be stationary and would move right or left...

I think the knot would move right and up after a quarter cycle...
The knot does not move left or right. It just goes up and down.

Take a look here
http://www.acoustics.salford.ac.uk/f...pes.htm#introd

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