AQA AS Physics Unit 2 (PHYA2) June 9th 2016 Resit paper Watch

WhoDaresWins
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#341
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#341
(Original post by McDerdactyl)
I got it was worse because the critical handle was smaller meaning less chance of total internal reflection? Brilliant there go more marks...
Thats so weird because I got the critical angle as smaller too, wtf?
You get a critical angle of like 22 or something?
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JamieOH
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#342
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(Original post by mbh16)
no because the supporting force is acting upwards
Yeah I know I had a retarded moment. Get it? But yeah I took moments about the rock with the kid acting down on the right and the weight acting down on the left. The moment of the weight was greater than moment of kid. So doesnt tilt.

Not correct?
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mbh16
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#343
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(Original post by gasman95)
Seen a few people here mention that the initial gradient of the truck (e.g. the acceleration)
would be greater. Surely, as the question stated that the water flowed out continuously across the entire journey, so therefore the initial mass would be the same and hence the same initial gradient as before.
I said that over time the acceleration would increase because F=ma so if F is constant but m is decreasing over time the a would increase, i don't know if this is correct though?
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JamieOH
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#344
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#344
(Original post by WhoDaresWins)
Thats so weird because I got the critical angle as smaller too, wtf?
You get a critical angle of like 22 or something?
Isnt there more chance of TIR if the angle is smaller lol...
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Billsonbubbles
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#345
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(Original post by mbh16)
well i think you will only lose one mark from doing that but it depends on whether u said that he would be supported or not to get most the marks
Cheers !

I stated the CW and ACW moment and said that as the rock provided the CW moment and the ACW came from the boy and the weight of the plank the CW was larger hence he could not walk to the end
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Billsonbubbles
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#346
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(Original post by mbh16)
I said that over time the acceleration would increase because F=ma so if F is constant but m is decreasing over time the a would increase, i don't know if this is correct though?
yes , that is correct. Though I stated that they would have the same driving force and be subject to the same resistance force which is why F is constant. However did you say they would reach the same speed because the forces acting would be equal at the same speed hence no acceleration, which means they would reach the same speed just the leaking truck would get there quicker.
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JamieOH
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#347
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(Original post by Pingu7)
The boys weight at the end of the plank would act down so the force of the plank on the other side will act up. picture a see saw and the rock as the pivot
I took the rock as the pivot
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mbh16
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#348
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(Original post by JamieOH)
Yeah I know I had a retarded moment. Get it? But yeah I took moments about the rock with the kid acting down on the right and the weight acting down on the left. The moment of the weight was greater than moment of kid. So doesnt tilt.

Not correct?
yeah i did it the same way as you, but i think you probably could have done it from the bank, if you worked out the upwards moment from the rock and then worked out the downwards moment of the boy and the plank, I'm not sure
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thatcooldude2.0
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#349
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#349
(Original post by Nerrad)
Did anyone get 2.9ms^-1 for the rocket question which means that the engine will manage to decelerate to the safe speed?
I did it the other way round but I see where you got that from. I calculated the force needed to decelerate it to its safe speed then it was less than 360( I think it was) so the engine will manage to decelerate it to its safe speed. Do you think that'll count too? I only realised I could've done it the other way round when the exam finished
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mbh16
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#350
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#350
(Original post by Billsonbubbles)
yes , that is correct
nice!, I have just thought though, the F won't be constant because as the lorry speeds up the F decreases
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JamieOH
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#351
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#351
(Original post by mbh16)
yeah i did it the same way as you, but i think you probably could have done it from the bank, if you worked out the upwards moment from the rock and then worked out the downwards moment of the boy and the plank, I'm not sure
Yes it may well work if you the plank and the boy vs. Rock
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thatcooldude2.0
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#352
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#352
Anyone else not finish the last 2 pages because of time?
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Nerrad
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#353
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(Original post by thatcooldude2.0)
I did it the other way round but I see where you got that from. I calculated the force needed to decelerate it to its safe speed then it was less than 360( I think it was) so the engine will manage to decelerate it to its safe speed. Do you think that'll count too? I only realised I could've done it the other way round when the exam finished
I think that's fine yea
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mbh16
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#354
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(Original post by Billsonbubbles)
yes , that is correct. Though I stated that they would have the same driving force and be subject to the same resistance force which is why F is constant. However did you say they would reach the same speed because the forces acting would be equal at the same speed hence no acceleration, which means they would reach the same speed just the leaking truck would get there quicker.
no, i was rushing but i put it wouldn't reach the same speed because F=ma and if the m was lower then the force would be lower but looking back at it it will reach the same speed because the m is lower but the a is higher
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philo-jitsu
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#355
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What were the other questions for the velocity one...

It was 5ms up and sin25....rearrange to get 11.83

Then i think one question was how high it travvelled which was done using suvat and i got 1.27m up or 1.3m rounded.

Another was horizontal distance travveled which was done by pythagorus of 11.83^2 -5^2 and sqroot to find horizontal speed....then times by flight time of 1.3s which gets s=13.9m

The diamonds ones i sped through so need help remembering....the second material had a higher refractive index...bare with
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WillRose
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#356
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#356
absolutely horredous exam

for the 6 marker i said the speed would end up greater as fricton between the tyres and the road is proportional to the reaction force, less reaction, less friction, greater end speed
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Nerrad
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(Original post by mbh16)
nice!, I have just thought though, the F won't be constant because as the lorry speeds up the F decreases
No the question clearly said that the driving force of the lorry is constant, therefore by Newton F=ma if m decreases a will increase, hence explains the increasing gradient at the first part of the graph, because it's accelerating
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UsmanM
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#358
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#358
(Original post by philo-jitsu)
What were the other questions for the velocity one...

It was 5ms up and sin25....rearrange to get 11.83

Then i think one question was how high it travvelled which was done using suvat and i got 1.27m up or 1.3m rounded.

Another was horizontal distance travveled which was done by pythagorus of 11.83^2 -5^2 and sqroot to find horizontal speed....then times by flight time of 1.3s which gets s=13.9m

The diamonds ones i sped through so need help remembering....the second material had a higher refractive index...bare with
I also got 1.3 to 2 sf.
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micycle
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#359
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#359
(Original post by mbh16)
how many times did you show TIR in the different shaped diamond?
This is how I drew it:

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mbh16
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#360
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#360
(Original post by Nerrad)
No the question clearly said that the driving force of the lorry is constant, therefore by Newton F=ma if m decreases a will increase, hence explains the increasing gradient at the first part of the graph, because it's accelerating
oh ok, but yeah the driving force is constant but the resultant force won't be cause of air resistance?
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