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# AQA Physics A - PHYA4 (11/06/12) - Exam thread Watch

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1. Just printed off every past paper from 2002. A LOT of the multi choice questions are repeated...i saw a question on a 02 paper that was exactly the same as one i had just done the other day on 10/11 paper! There are questions on waves that are useless though. Now to do them all
2. Can anyone confirm if these phase differences for SHM are correct? Would really appreciate it!

Velocity and displacement = pi/2
Velocity and acceleration = pi/2
Acceleration and displacement = pi
3. (Original post by don'tTRIP.)
Can anyone confirm if these phase differences for SHM are correct? Would really appreciate it!

Velocity and displacement = pi/2
Velocity and acceleration = pi/2
Acceleration and displacement = pi

velocity and displacement=pi/2
acceleration and displacement=pi
velocity and acceleration=pi/2

yep
4. For anyone who needs help with electromagnetic induction

5. what do you need to know for this unit?

may sound like a stupid question, but what i mean is, the majority of stuff is equations that we're given, so what knowledge based stuff do we need?
6. (Original post by Funky Monk)
Think this should work, here are the ones for Unit 4
thanks!!!
7. (Original post by sconter)
what do you need to know for this unit?

may sound like a stupid question, but what i mean is, the majority of stuff is equations that we're given, so what knowledge based stuff do we need?
the main theories:
• conservation of momentum
• circular motion
• conditions of shm
• resonance
• satellite motion
• magetic fields causing circular orbits
• wire/coil in magnetic field

then the rest i think is mainly mathsy stuff
you could youtube the topics above to get a good idea of them
8. can someone pls help me with this question??

A simple pendulum and a mass-spring system are taken to the Moon, where the gravitational field strength is less than on Earth. Which line, A to D, correctly describes the change, if any, in the period when compared with its value on Earth?

period of pendulum period of mass-spring system
A. decrease decrease
B. increase increase
C. no change decrease
D. increase no change

The correct answer is apparently D, but I thought that the period of mass-spring system would also be affected since T = 2(pi) x square root of (m/k), and k (spring constant) is affected by the force applied (F=k x extension ; F=mg) , if g decreases on the moon then F would also decrease, causing k to decrease. :/ Someone pls clear this up for me!! thanks
9. (Original post by Meh_)
can someone pls help me with this question??

A simple pendulum and a mass-spring system are taken to the Moon, where the gravitational field strength is less than on Earth. Which line, A to D, correctly describes the change, if any, in the period when compared with its value on Earth?

period of pendulum period of mass-spring system
A. decrease decrease
B. increase increase
C. no change decrease
D. increase no change

The correct answer is apparently D, but I thought that the period of mass-spring system would also be affected since T = 2(pi) x square root of (m/k), and k (spring constant) is affected by the force applied (F=k x extension ; F=mg) , if g decreases on the moon then F would also decrease, causing k to decrease. :/ Someone pls clear this up for me!! thanks
I would have circled B in the exam too, but now I think about it a mass-spring system undergoes simple harmonic motion (force isn't in the period equation for starters), so, the period is unchanged when the force changes.

For this question it's better to look at it just at the equations, but I can understand why you thought D is a wrong answer.

Does anyone want to compile a list of words/sentences of things you should and shouldn't say?

Value Magnitude
It [noun]
Talk about external forces as much as possible (especially for SHM)
Remember newtons 1st,2nd,3rd law

Can't think of anymore but I'm sure you guys have some!
10. (Original post by Meh_)
can someone pls help me with this question??

A simple pendulum and a mass-spring system are taken to the Moon, where the gravitational field strength is less than on Earth. Which line, A to D, correctly describes the change, if any, in the period when compared with its value on Earth?

period of pendulum period of mass-spring system
A. decrease decrease
B. increase increase
C. no change decrease
D. increase no change

The correct answer is apparently D, but I thought that the period of mass-spring system would also be affected since T = 2(pi) x square root of (m/k), and k (spring constant) is affected by the force applied (F=k x extension ; F=mg) , if g decreases on the moon then F would also decrease, causing k to decrease. :/ Someone pls clear this up for me!! thanks
First instinct for me was to circle D, the reason for that is because when they are telling you about the time period for either a mass spring or pendulum question you've got to instantly think about those two equations for T for each one. Only one of them is actually affected by g. I see what you mean with F=mg= kL however the spring constant, is a constant.
Also Force is not included in the T equation, as the previous person said.

Just looking at the mass-spring changes, there is only one that says "no change" and we know that there shouldn't be a change. So even without considering the time period for the pendulum we can say it is D.

If you want to consider the pendulum version of the equation to be on the safe side, you can see by the equation that T should be inversly proportional to sqrt g right? So with g decreasing. T would have to increase.

I hope that helped
11. Can someone help me with this please,

Explain why the frequency of the periodic force needs to be equal to the oscillating system's natural frequency to cause resonance.

^ I know thats a very simple question, but I just don't know how to phrase my explanation.
12. (Original post by internet tough guy)
Can someone help me with this please,

Explain why the frequency of the periodic force needs to be equal to the oscillating system's natural frequency to cause resonance.

^ I know thats a very simple question, but I just don't know how to phrase my explanation.
Well resonance is caused when the driving frequency is equal to the system's natural frequency. So i think the question is just testing for if you know how resonance is caused. how many marks is it worth?
13. (Original post by internet tough guy)
Can someone help me with this please,

Explain why the frequency of the periodic force needs to be equal to the oscillating system's natural frequency to cause resonance.

^ I know thats a very simple question, but I just don't know how to phrase my explanation.
When the frequency of the external periodic force matches the natural frequency, there is efficient energy transfer from external to natural. The periodic frequency wave will be precisely 1/4 of a wavelength out of phase to the natural frequency and the external force will give the oscillating system extra force whenever the natural amplitude is not zero.

not really sure about that one
14. (Original post by m1a1tank)
Well resonance is caused when the driving frequency is equal to the system's natural frequency. So i think the question is just testing for if you know how resonance is caused. how many marks is it worth?
Yeah I know that, I just don't know how to put my understanding into words, I'm not very good an explaining concepts. Btw its just a summary question from the textbook
15. Could someone explain to me why Q16 on Jan 2012 multiple choice is D?
16. (Original post by don'tTRIP.)
Could someone explain to me why Q16 on Jan 2012 multiple choice is D?
Well its asking for which ones CAN NOT be used right. You know that E= V/d

So that gives you a volt per metre as the units. We also know that a volt is the same as a joule per coloumb.

So A has to be correct. The way i look at these questions is they always give 4 options, two of which are incredibly similiar. In this case both A and D are very similar. So lets just assume that B and C are correct too then.

Now i just need to see which is right out of A and D. In this case A can be. Therefore D can not be.
17. What exactly is the unit for 'g' the gravitational field strength?

I mean, its acceleration isn't it? so isn't it ms^-2 instead of Nkg^-1 ???
18. (Original post by internet tough guy)
What exactly is the unit for 'g' the gravitational field strength?

I mean, its acceleration isn't it? so isn't it ms^-2 instead of Nkg^-1 ???
It is ms^-2 but it can also be Nkg^-1

Remember F=Ma, so because a=g, F=Mg
Rearrange that and you have g=F/M which is a N/kg aka Nkg^-1
19. (Original post by m1a1tank)
It is ms^-2 but it can also be Nkg^-1

Remember F=Ma, so because a=g, F=Mg
Rearrange that and you have g=F/M which is a N/kg aka Nkg^-1
do you think i'll lose a mark for putting ms^-2 instead of Nkg^-1 as the my unit for gravitional field strength?
20. (Original post by internet tough guy)
do you think i'll lose a mark for putting ms^-2 instead of Nkg^-1 as the my unit for gravitional field strength?
which question is this in the paper?

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