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# The Physics PHYA2 thread! 5th June 2013 watch

• View Poll Results: What mark do you think you got out of 70?
0-20
6
3.00%
21-40
12
6.00%
41-50
29
14.50%
51-60
79
39.50%
61-70
74
37.00%

1. (Original post by `Jts)
Only thing I'm not 100% on is the 6 marker. Anyone have any brief ideas on what it could be?
Nope

I was expecting something generic for unit 1, and then look at what we got for that!

I'd assume that they are going to do the same, so I have a horrible feeling they will do it on diffraction gratings or energy conversions. Or less likely, they will give us the standard 6 marker of describe an experiment, which is just to state what was mentioned a couple of pages back.
2. (Original post by StalkeR47)
you mention the change is velocity will affect the horizontal motion. That is correct. But, if you say velocity will change the horizontal motion, that is incorrect. Ship changing speed would mean that the drag force from the water is increased and so the air resistance, so it is a factor that causes change in the horizontal force/motion.
What I don't get is why the mark scheme says that "acceleration/speed of the ship" is a correct answer to question 1c on the paper. Please could you explain this? How can the ship's speed affect the horizontal component of the force exerted on the ship by the sail?
3. do you guys think we need to know how to derive the fringe spacing and diffraction angle equation?
4. (Original post by Jack93o)
do you guys think we need to know how to derive the fringe spacing and diffraction angle equation?
well since the syllabus says we need to know how to derive diffraction grating, im guessing we need to know that one lool, but i dont think we need to know for the fringe spacing, but that can be done too anyways
5. (Original post by masryboy94)
question: what is the difference from saying you get a maxima\minima or bright\dark fringes or zero\first order?
maxima/minima can happen in both experiments while bright/dark fringes is fringe spacing, I think
6. (Original post by Claree)
What I don't get is why the mark scheme says that "acceleration/speed of the ship" is a correct answer to question 1c on the paper. Please could you explain this? How can the ship's speed affect the horizontal component of the force exerted on the ship by the sail?
Think about. If you increase the speed, there is more air resistance and the drag (water) force. If you decrease the speed, there is less air resistance and the drag force from the water. Ship if moving horizontally, not vertically. So, these factors would affect the horizontal motion of the ship.
7. (Original post by Qari)
maxima/minima can happen in both experiments while bright/dark fringes is fringe spacing, I think
but isnt a maxima a bright fringe which is the n order? and likewise for minima?
8. (Original post by OliverG)
Nope

I was expecting something generic for unit 1, and then look at what we got for that!

I'd assume that they are going to do the same, so I have a horrible feeling they will do it on diffraction gratings or energy conversions. Or less likely, they will give us the standard 6 marker of describe an experiment, which is just to state what was mentioned a couple of pages back.
Oh alright. Thanks!
9. (Original post by Claree)
What I don't get is why the mark scheme says that "acceleration/speed of the ship" is a correct answer to question 1c on the paper. Please could you explain this? How can the ship's speed affect the horizontal component of the force exerted on the ship by the sail?
Greater the speed, it's moving the more resistance on the sail

a=v/t

F=ma or F=mv/t meaning force is proportional to velocity, so as one increases so does the other
10. (Original post by StalkeR47)
Think about. If you increase the speed, there is more air resistance and the drag (water) force. If you decrease the speed, there is less air resistance and the drag force from the water. Ship if moving horizontally, not vertically. So, these factors would affect the horizontal motion of the ship.
Doesn't the question want you to refer to the effect on the "horizontal force" on the ship exerted by the sail, not the ship's "horizontal motion"?
11. (Original post by Qari)
maxima/minima can happen in both experiments while bright/dark fringes is fringe spacing, I think
Dark/bright fringes are not the fringe spacing. Max is called bright and min is called the dark. There is no difference.
12. This is a really stupid question but what are the rearrangements of the dsintheta=nlambda?

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13. (Original post by Qari)
Greater the speed, it's moving the more resistance on the sail

a=v/t

F=ma or F=mv/t meaning force is proportional to velocity, so as one increases so does the other
Thanks!!! I understand now
14. can someone please tell me how many significant figures we're meant to go to? Physics is so vague
15. (Original post by Claree)
Doesn't the question want you to refer to the effect on the "horizontal force" on the ship exerted by the sail, not the ship's "horizontal motion"?
Force affects the motion. So it is the same thing. And, you can just state increasing the speed- would be 1 factor. Wind force is another factor.
16. (Original post by Qari)
Greater the speed, it's moving the more resistance on the sail

a=v/t

F=ma or F=mv/t meaning force is proportional to velocity, so as one increases so does the other
So does that mean that the force exerted on the ship by the sails increases as the ship accelerates?
17. (Original post by masryboy94)
but isnt a maxima a bright fringe which is the n order? and likewise for minima?
What do you mean n order.
And maxima is where peak and peak meet
18. Can someone please explain how phase difference works on stationary waves please
19. (Original post by Claree)
So does that mean that the force exerted on the ship by the sails increases as the ship accelerates?
Yes
20. (Original post by Claree)
Thanks!!! I understand now
So in summary, whenever you're faced with these questions, think of Newtons laws of motion and apply it to the question.

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