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Edexcel Physics Unit 1 17th May 2012

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    (Original post by Top Hats)
    Density = (mass)/(volume) ---> mass = (density)(volume)

    Density is same for all objects (as stated in question)

    The pebbles have a larger diameter, therefore they have a larger volume. From the equation above, this means they have a greater mass.

    Weight = (mass)(acceleration due to gravity)

    Pebbles have a larger mass; equation above shows that is means they have a greater force of weight acting downwards.

    Force = (mass)(acceleration) ---> acceleration = (force)/(mass)

    Equation above shows that this means they accelerate downwards faster (due to the greater force of gravity), and therefore they reach the bottom of the jar first.
    I wrote an answer similar to this using mass=density x volume (similar to what you wrote) but didnt mention the other equation (force=massxacceleration). Did the question ask why it accelerated faster or did it just ask why it was at the bottom?
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    (Original post by Username_valid)
    I wrote an answer similar to this using mass=density x volume (similar to what you wrote) but didnt mention the other equation (force=massxacceleration). Did the question ask why it accelerated faster or did it just ask why it was at the bottom?
    If I remember correctly, the question was why it reached the bottom. However, the reason why the pebbles reached the bottom, was because they accelerated the fastest and therefore reached the bottom first.
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    (Original post by Sagacious)
    But surely you would have to mention the up-thrust and viscous drag? As the radius is increased, the resistive forces increase, hence this would decrease the resultant force? Therefore, acceleration would decrease.
    It's all about magnitude. The force of upthrust is equal to the weight of the fluid (in this case water) that is displaced. The volume of the fluid displaced and the volume of the pebble are equal. However, the density of the pebble is greater than the density of the water.

    Mass = (density)(volume)

    Therefore, the pebble will have a greater mass than the mass of the fluid displaced.

    Weight = (mass)(acceleration due to gravity)

    Therefore, the force of the pebble's weight will be greater than the force of the displaced water's weight. Hence, the resultant downward force will be greater.
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    (Original post by Top Hats)
    If I remember correctly, the question was why it reached the bottom. However, the reason why the pebbles reached the bottom, was because they accelerated the fastest and therefore reached the bottom first.
    oh god i wrote the same thing. i was going to leave that question but then said : "no i should at least try it" cz even edexcel people say this: "try to solve every question" I did write the answer in more detail so i could convince the examiners........phewwww
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    (Original post by shahlakh)
    oh god i wrote the same thing. i was going to leave that question but then said : "no i should at least try it" cz even edexcel people say this: "try to solve every question" I did write the answer in more detail so i could convince the examiners........phewwww
    Nice!

    You should always attempt every question.
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    So there's never going to be an unofficial mark scheme then?
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    (Original post by Top Hats)
    Nice!

    You should always attempt every question.
    hahahah thanks........
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    (Original post by AGrumpyMole)
    So there's never going to be an unofficial mark scheme then?
    yeah i think so. cz u know in the previous papers there were no unofficial mark schemes for any subjects except maths. so why not now?
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    Right people, it's time to forget about this paper now and move onto unit 2 revision for most of us; onward and upward!

    Good luck for your remaining exams everyone
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    (Original post by Top Hats)
    It's all about magnitude. The force of upthrust is equal to the weight of the fluid (in this case water) that is displaced. The volume of the fluid displaced and the volume of the pebble are equal. However, the density of the pebble is greater than the density of the water.

    Mass = (density)(volume)

    Therefore, the pebble will have a greater mass than the mass of the fluid displaced.

    Weight = (mass)(acceleration due to gravity)

    Therefore, the force of the pebble's weight will be greater than the force of the displaced water's weight. Hence, the resultant downward force will be greater.
    I used the formula: v_term=[2g(density_rock-density_water)/9n]x r^2

    so the whole thing in [... ] is a constant, while v_term increase as the radius increase.

    Our approach are more or less similar, however, I don't know if the marker would accept me directly using this formula without proving it :-(
    :finger cross:
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    (Original post by youlostme)
    do you guys think they would give a 60+ grade boundary for an A?
    i mean, considering how easy the paper was...
    I spoke to my physics teachers and asked how the Year 12s found it (I'm in Year 13, re-sitting this paper) and the general feedback was that they found it quite difficult. At least, not as easy as everyone has made out on here. And they're quite a clever group. Maybe/hopefully grade boundaries won't be too high - remember people on STR are often more clever than the average A-level student!
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    (Original post by britchick)
    I spoke to my physics teachers and asked how the Year 12s found it (I'm in Year 13, re-sitting this paper) and the general feedback was that they found it quite difficult. At least, not as easy as everyone has made out on here. And they're quite a clever group. Maybe/hopefully grade boundaries won't be too high - remember people on STR are often more clever than the average A-level student!
    very true.. i agree.. the grade boundaries might be lower.. so no need to worry much.. coz the people who told the paper was easy could have made silly mistakes.. who knows what the answers would be..
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    Mark scheme?
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    ya can sum 1 pls put up the mrkscehme?? :/ my unit 2 exm ws supeer bad....jst hoping to do well in this one...
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    (Original post by chow1994)
    ya can sum 1 pls put up the mrkscehme?? :/ my unit 2 exm ws supeer bad....jst hoping to do well in this one...
    F*** me that exam was a b****. It was soo hard.
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    unit2 was insane. left out the entire last question
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    3RD RESIT FOR UNIT 2 HERE I COMEEEEEEEEEE what the **** was that i honestly had nooo cluee on some of the questions i think the only thing i did well on was multiple choice and the definitions
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    How could the UNIT 2 paper be so difficult!?!?!?!? the last question was imposible! how I a suposed to know that!
    and in the first question after the multiple choice, wasnt switch B useless??
    really weird exam, hate electricity and halve of the paper on electricity! so lucky!
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    Y was it so hard??God nooo....my hopes..all ruined..Unit 2 was damn hard..Last qustion 10 mark gone ...some marks gone in mcq,,why did we use computer in the last mcq??..Guys does the diameter of wire comes .028mm???

    and also what is the answer about the last mercury tube question u knw about the phosphorus absorbing photons...i said that it emits photon of diff frequency so we can see it..??Is it wrong?
    I sincerely hope A is below 55 or sth..
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    any1 hav ne idea wht da gradeboundary wud b dis tym in unit-1...nd ne1 has da solution of da paper???

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