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OCR Physics A Breadth of Physics (24th May 2016) Discussion

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The multiple choice question, i think it was questiom 6, it said what graph resembles this force time graph and it was a curve, i guessed kinetic energy graph

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Original post by santos668
How do you get equal 8 but I get 16 😞 whare I found gradient equal to 16


It should be 16 as u^2 was m^2s^-2 and x was m so u^2÷x is ms^-2 which is acceleration
For the mulitple choice,

Was question two (the thing lifting up a weight), the vertical height times the weight.

And for the question about those two trolley colliding, was the answer A (momentum is conserved).

Also was an answer towards the end 16 about the ratios of elasicpotential energy?
Original post by Fish40
The multiple choice question, i think it was questiom 6, it said what graph resembles this force time graph and it was a curve, i guessed kinetic energy graph

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i put momentum as the area under a ft graph is equal to the momentum
Original post by Fish40
The multiple choice question, i think it was questiom 6, it said what graph resembles this force time graph and it was a curve, i guessed kinetic energy graph

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was there an option for acceleration/time? I thought the change in F would create a proportional change in A because the M in F=MA is constant.
Original post by Fish40
Gradient i got was 400/25 = 16 as m^2s^-2 divided by m = ms^-2

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It said the relationship is u^2=2ax so you have to divide by two.
if you cross something out in a way that you can still read the answer underneath, that doesnt count right? I messed up the 4 marker about the pressure of the cylinder by overthinking it
Original post by julesaquilina
i put momentum as the area under a ft graph is equal to the momentum


Yeah thinks its moentum, and as momentums conserved, the graphs goes from 0 up then back to 0 so momentums conserved

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Original post by julesaquilina
if you cross something out in a way that you can still read the answer underneath, that doesnt count right? I messed up the 4 marker about the pressure of the cylinder by overthinking it


if they can read it they can still award you marks for it
Original post by viktorh
was there an option for acceleration/time? I thought the change in F would create a proportional change in A because the M in F=MA is constant.


I did acceleration as well bexause its constant
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Avatar for Oooskar
Oooskar
For the multiple choice potential divider question can someone explain how this method is wrong? The pd across the resistor in parallel with the circuit AB is 9*(3000/4000)=6.75V (emf=9V, this resistor=3000 ohms, other resistor=1000 ohms). The current in the circuit AB is 1mA so the power in the circuit AB is P=IV=6.75mW, I ended up putting 6mW which apparently is the correct answer anyway but I would just like to know where the flaw is in my method.

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Did anyone get 750kgm^-3 for the cylinder density?
Original post by julesaquilina
if you cross something out in a way that you can still read the answer underneath, that doesnt count right? I messed up the 4 marker about the pressure of the cylinder by overthinking it


Yeah if you didn't write anything else. What was the answer? I just put weigh the cylinder on scales, and the area calculated using pie r^2. Wasn't sure about the error though.
Original post by viktorh
Did all you 70 people remember to use a negative value for velocity when the particle was going in the other direction?


****
Original post by Parhomus
It said the relationship is u^2=2ax so you have to divide by two.


Your right :frown:

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Original post by Oooskar
For the multiple choice potential divider question can someone explain how this method is wrong? The pd across the resistor in parallel with the circuit AB is 9*(3000/4000)=6.75V (emf=9V, this resistor=3000 ohms, other resistor=1000 ohms). The current in the circuit AB is 1mA so the power in the circuit AB is P=IV=6.75mW, I ended up putting 6mW which apparently is the correct answer anyway but I would just like to know where the flaw is in my method.

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Oh I thought it was the current in the resistor branch which I thought was 2 :frown: Oh well.
Original post by yelash
Yeah if you didn't write anything else. What was the answer? I just put weigh the cylinder on scales, and the area calculated using pie r^2. Wasn't sure about the error though.


I mentioned about the area being pi r^2 but then i crossed it outtttt, and i spoke about weighing the cylinder on a balance and multiplying by 9.81 for the force
Original post by sddsfsdafs
Did anyone get 750kgm^-3 for the cylinder density?


yep
Original post by Oooskar
For the multiple choice potential divider question can someone explain how this method is wrong? The pd across the resistor in parallel with the circuit AB is 9*(3000/4000)=6.75V (emf=9V, this resistor=3000 ohms, other resistor=1000 ohms). The current in the circuit AB is 1mA so the power in the circuit AB is P=IV=6.75mW, I ended up putting 6mW which apparently is the correct answer anyway but I would just like to know where the flaw is in my method.

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I think that didnt work because you didn't take into fact the possible resistance of the extra branch and so the actual Vout would be different. But yh i got 6 too
Original post by SalazarSlytherin
****


yes

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