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G481 Mechanics 20 May 2014 Unoffical mark scheme

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I feel as though I may be missing something here so I am happy to be proven wrong! Here goes:

Surely in the terminal velocity question if the two objects have different terminal velocities then the one with a higher TV will hit the ground first. But this completely contradicts Galileos experiment which showed that all objects hit the ground at the same time, regardless of mass??

please explain because I'm massively confused about this!! Thanks
Reply 81
Original post by Belle95
Very petty question : but on the 6d section where you had to work out efficiency, did it say 'percentage efficiency' in the question? Because I think I stupidly put 20 without the '%' :frown:


The % sign was included after the answer space. You're fine.
Reply 82
Original post by dedwards.96
I feel as though I may be missing something here so I am happy to be proven wrong! Here goes:

Surely in the terminal velocity question if the two objects have different terminal velocities then the one with a higher TV will hit the ground first. But this completely contradicts Galileos experiment which showed that all objects hit the ground at the same time, regardless of mass??

please explain because I'm massively confused about this!! Thanks


I had the same problem earlier trying to get my head around it. But I understand now (and someone please correct me if I'm wrong) that Galileo's experiment showed that everything accelerates at the same rate, nothing to do with Terminal Velocity, as in these experiments, the objects never reached such speeds.
In this question, the table tennis ball will reach its TV faster, as the drag force required to counter-act its weight is less than that of the golf ball. Until this point, the two balls will have dropped equal distance, but afterwards the Golf ball will continue accelerating as it need a greater velocity to create more drag to counteract its larger weight. Meaning that the golf ball will travel quicker at its TV.
Reply 83
NEED some help, thats what ive written for quiestion 6, how many marks do I get?
do i get any ECF ??

6a) WD = force x distance moved in direction of force
b) work done against friction
c) 1W = 1 joule per second
d) Rate of doing work = Fs= 75x5200x9.81= 3.8x10^6
so rate = 75x5200x9.81 / (1.5 x 60) = 42510
Efficiciency = Pout/ Pin x 100% = 42510/170E3 x100 = 25%
(edited 9 years ago)
Was the terminal velocity question a golf ball or a gold ball cause I thought it was golf but literally everyone has put gold??


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Original post by WillowXxx
Was the terminal velocity question a golf ball or a gold ball cause I thought it was golf but literally everyone has put gold??


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I thought it was golf at the time, but now I'm not so sure :colondollar:


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Thank you for this - think I got 49 - possibly 52 as I can't remember what I did for the second to last question - thought I got 0.16J but now rethinking it...
Reply 87
Original post by Belle95
Very petty question : but on the 6d section where you had to work out efficiency, did it say 'percentage efficiency' in the question? Because I think I stupidly put 20 without the '%' :frown:

You''ll be Ok. The % was given in the answer space.
Reply 88
Original post by dedwards.96
I feel as though I may be missing something here so I am happy to be proven wrong! Here goes:

Surely in the terminal velocity question if the two objects have different terminal velocities then the one with a higher TV will hit the ground first. But this completely contradicts Galileos experiment which showed that all objects hit the ground at the same time, regardless of mass??

please explain because I'm massively confused about this!! Thanks


Galileo applies in the absence of air resistance.

Aristotle was right when air resistance applies ie heavier objects hit first. Pretty easy to check by experiment!
Reply 89
Original post by sg_1108
Can you define velocity as displacement over time?


No - this is average velocity
How many marks would I lose if I said golf ball instead of gold ball??
I'm fairly sure it said golf ball and not gold ball? maybe we're missing something
Original post by Jamborambowambo
I'm fairly sure it said golf ball and not gold ball? maybe we're missing something


Are you sure because a lot of people are saying gold ball, heck, even the thread starter said gold ball in his answer. I scared. :C
Reply 93
For the question about terminal velocity, I said 'tennis ball' instead of gold ball because I must have mixed the gold ball up somehow with a different ball. Anyway, I gave the correct reasoning - greater mass, therefore greater weight and greater drag, will I still get the 3 marks for the question?
Original post by sagar448
Are you sure because a lot of people are saying gold ball, heck, even the thread starter said gold ball in his answer. I scared. :C


If there is this much confusion then there might be some leniency with the marking, maybe gold/golf/table tennis were all mentioned just on different questions and people got mixed up/misread?
Original post by Jamborambowambo
If there is this much confusion then there might be some leniency with the marking, maybe gold/golf/table tennis were all mentioned just on different questions and people got mixed up/misread?


True but what did you write golf ball or gold ball? I mean I am pretty sure I read golf ball and I didn't see a gold ball any where on the paper. I've already lost around 10 marks and losing anymore would cost me my A grade. :C
Hello,
Please could you tell me are there 2 possible answers for the second last one ? Because theres 2 equations for springs energy - e=kxsqared and e=0.5xfxX. I used the latter and got 0.06 along along with some of my friends, is this right or how many marks will I get for it?
Thanks
Most people doing G491 didn't manage to finish so well done folks :smile:


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Reply 98
Original post by randlemcmurphy
Are these estimates at the highest you think they could be, or the lowest?


Although I'm not a teacher, I seriously doubt it would be 45/60 for an A. It should be around 41/42 in my opinion because I've done all the past papers (legacy too) and this was the hardest paper for numerous reasons. I don't see why it shouldn't be around 42 because every year there are year 13s who re-sit the G481 paper, so even if quite a few year 13s sat this paper it shouldn't make a major difference
Original post by teacher607
Hello,
Please could you tell me are there 2 possible answers for the second last one ? Because theres 2 equations for springs energy - e=kxsqared and e=0.5xfxX. I used the latter and got 0.06 along along with some of my friends, is this right or how many marks will I get for it?
Thanks


Answer was 0.16 since E = 1/2kx^2 for the spring with extension 6cm you get 0.09 and for the spring with the extension 10cm you get 0.25 and so 0.25 - 0.09 you get 0.16j

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