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AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread] Watch

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    RATE of change of momentum is a force which was weight it really isn't too hard
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    (Original post by joesterman)
    What did you guys get on the written for the number of degrees the lead ball turned through? I got 131 or something similar?
    Same, and I know two others who got this
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    (Original post by mrno1324)
    Do you remember how the questions was worded?
    No sorry :c.
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    (Original post by Mehrdad jafari)
    The rate of change of momentum is acceleration. A body cannot accelerate if it's momentum doesn't change


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    No, force = rate of change momentum look up newton's 2nd law

    if you don't believe newton Force = Mass x Acceleration = Kg x Ms-2 = N!!!!!!

    by saying unit of force = unit of acceleration you're saying that Mass has no unit, which is totally wrong
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    Also for the electron question why are people saying the number halves? To 2.2x10 to the something
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    (Original post by Mehrdad jafari)
    The rate of change of momentum is acceleration. A body cannot accelerate if it's momentum doesn't change


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    But the unit of rate of change of momentum is Newtons as it equals Force. So how can it be acceleration. I do not understand
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    (Original post by M1llward)
    The Electric field strength should have been negative as the charge was negative. -1560 Vm^-1.

    I got this wrong.

    Also any clues on the damping question? I wrote there would be more damping without the ring as the total energy given to the system with the ring will be greater as GPE=mgh. The work done against air resistance is the same as time period is not affected - because the pendulum system has more energy with the ring it will take longer for the initial energy to be lost through doing work against air resistance. Thus the amplitude will decrease at a slower rate.
    Your answer makes sense assuming the initial displacement of both was the same and it wasn't pushed by a force(to its initial displacement). I can't remember if it mentioned this.
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    (Original post by king cobra)
    Did people get 1.4 for the height ?


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    yes

    (Original post by Ruyshi)
    Surely the ring has no effect on damping... It was placed in such a way that no extra surface area was provided to the cone.. so no effect on air resistance..
    time period is no different, so velocity is no difference and so again air resistance does not change..
    I said what you did but I realise its wrong

    light damping has no effect on the time period because Amplitude is not related to time period, but with damping the amplitude generally increases

    heavier damping should be with the ring on i think
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    For the coil with a power supply and ammeter, which way should the needle have initially gone? And which way should it have gone in the next part?
    I explained using lens's law and faradays law, did anyone else do this?
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    (Original post by Greg213)
    Yep
    Don't you get 4mJ from the battery and then minus 2mj to get the energy used up which is 2. So B couldn't havw been incorrect.
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    (Original post by Alexie56)
    Only the discharge was using a different resistor, i think they wanted you to assume they start at the same current. Then they just increased resistance. I'm not too sure but I don't think they would've made a typo.
    I don't quite understand: There is nothing to assume here, everything can be calculated. The current in a circuit is affected by the load resistance and the electrical energy supplied by the battery. In this situation, electrical energy, i.e. voltage, supplied is the same, but the load resistance is higher. Therefore, this causes the current to decreases as there is more opposition to it in the circuit.
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    First question 10000% was weight, by laws of dimensional analysis 😋
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    What was the capacitance curve supposed to be? I didn't even register that one of them was supposedly 'k' ohms
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    (Original post by TheRAG)
    So do you think B is correct then?
    Whichever one had the largest area. I remember it being a square with side length 0.5. If that one was option B then yes, B is correct.
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    (Original post by NEWT0N)
    Yes, and KE is proportional to v^2 since the factor of 0.5m is constant since both are electrons and therefore have the same mass m.

    Kinetic energy of x is twice that of y, hence v_x^2=0.5v_y^2 by what I just said. Hence \frac{v_x}{v_y}=\sqrt{0.5}.

    Now, the field exerts a force of F=BQv on a charge Q moving at right angles to the field with velocity v. BQ is the same for both electrons for obvious reasons, so F is proportional to v. Therefore, \frac{F_x}{F_y}=\frac{v_x}{v_y}=  \sqrt{0.5} which is the same as \frac{1}{\sqrt{2}}. (option B I think)
    I got that too! And i think it was option C but it doesnt matter
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    (Original post by NEWT0N)
    Yes, and KE is proportional to v^2 since the factor of 0.5m is constant since both are electrons and therefore have the same mass m.

    Kinetic energy of x is twice that of y, hence v_x^2=0.5v_y^2 by what I just said. Hence \frac{v_x}{v_y}=\sqrt{0.5}.

    Now, the field exerts a force of F=BQv on a charge Q moving at right angles to the field with velocity v. BQ is the same for both electrons for obvious reasons, so F is proportional to v. Therefore, \frac{F_x}{F_y}=\frac{v_x}{v_y}=  \sqrt{0.5} which is the same as \frac{1}{\sqrt{2}}. (option B I think)
    Yeah, might be the one for that question


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    (Original post by TheRAG)
    For Coulombs law, would I get any marks for quoting the formula and saying what each symbol meant?
    Yeah they've accepted that in past papers so should be fine

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    Name:  ImageUploadedByStudent Room1434021396.113753.jpg
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    My multi choice, might not have done well though
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    (Original post by Humbers)
    No, force = rate of change momentum look up newton's 2nd law

    if you don't believe newton Force = Mass x Acceleration = Kg x Ms-2 = N!!!!!!

    by saying unit of force = unit of acceleration you're saying that Mass has no unit, which is totally wrong
    So the answer should have been weight?
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    (Original post by Disney0702)
    But the unit of rate of change of momentum is Newtons as it equals Force. So how can it be acceleration. I do not understand

    It isn't acceleration the guy you quoted got it wrong. You are right rate of change of momentum is force which has the unit Newtons
 
 
 
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