Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    2
    ReputationRep:
    http://filestore.aqa.org.uk/subjects...W-QP-JUN10.PDF

    Question 4b(i)

    So I thought that GPE lost = KE gained so surely as it comes back down 3.2m then it would just be 3.2 * 9.81 * 55 = 1726.56 J?

    The mark scheme says this however

    (Ek = 3.2/4.2 x 2264 or uses suitable kinematics equation)1= 1700(J) ! (= 1724.8 = 1720)

    I don't understand why they divided 3.2/4.2 at all. Can anyone explain?
    Thanks
    • Thread Starter
    Offline

    2
    ReputationRep:
    Any ideas?
    • Study Helper
    Offline

    21
    ReputationRep:
    Study Helper
    (Original post by CrazyFool229)
    http://filestore.aqa.org.uk/subjects...W-QP-JUN10.PDF

    Question 4b(i)

    So I thought that GPE lost = KE gained so surely as it comes back down 3.2m then it would just be 3.2 * 9.81 * 55 = 1726.56 J?

    The mark scheme says this however

    (Ek = 3.2/4.2 x 2264 or uses suitable kinematics equation)1= 1700(J) ! (= 1724.8 = 1720)

    I don't understand why they divided 3.2/4.2 at all. Can anyone explain?
    Thanks
    mgh = 55 x 9.81 x 4.2 = 2266 Joules

    GPE lost = 55 x 9.81 x 3.2 = 1726.56 Joules

    In other words, the mark scheme simply cancels out the 4.2m to avoid writing the whole expression again.

    i.e.

    GPE lost = \frac{3.2}{4.2} \rm \ x \ 2266 = 3.2 \rm \frac{(55 x 9.81 x 4.2)}{4.2} = 3.2\ x \ 55\ x \ 9.81
    • Thread Starter
    Offline

    2
    ReputationRep:
    Thanks for the reply!

    So it seems like you did the same equation as me but for some reason the answer is still different to the mark scheme? Sorry if this is stupid as I know it is only one mark!

    [SIZE=1]Posted from TSR Mobile[/SIZE
    • Thread Starter
    Offline

    2
    ReputationRep:
    I just noticed that the mark scheme used a different energy rather than the one calculated which will affect the answer. Is there a reason for that also?

    Posted from TSR Mobile
    • Study Helper
    Offline

    21
    ReputationRep:
    Study Helper
    (Original post by CrazyFool229)
    I just noticed that the mark scheme used a different energy rather than the one calculated which will affect the answer. Is there a reason for that also?

    Posted from TSR Mobile
    It's the same, they just rounded it to 1700J which tells other markers that rounding is acceptable in this instance since it's the method they are after.
    • Thread Starter
    Offline

    2
    ReputationRep:
    Oh I see now! Mark schemes can be a little confusing for me sometimes

    Thank you so much for your help

    Posted from TSR Mobile
    • Study Helper
    Offline

    21
    ReputationRep:
    Study Helper
    (Original post by CrazyFool229)
    Oh I see now! Mark schemes can be a little confusing for me sometimes

    Thank you so much for your help

    Posted from TSR Mobile
    No worries.

    Mark schemes are not produced for students. They are there for the army of markers who will all have a suitable qualification in Physics and Maths and therefore it's an aid for them to get consistency between each other. The fact that students can get access to them is helpful to an extent but also causes confusion as you have discovered!
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Would you like to hibernate through the winter months?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.