Join TSR now and get all your revision questions answeredSign up now

AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread] Watch

    Offline

    2
    ReputationRep:
    Name:  ImageUploadedByStudent Room1433630613.964493.jpg
Views: 72
Size:  77.7 KB

    I'm struggling with this one too


    Posted from TSR Mobile
    Offline

    16
    ReputationRep:
    (Original post by gcsestuff)
    Attachment 420941

    I keep getting B, any help ?


    Posted from TSR Mobile
    It should be the maximum flux linkage, shouldn't it? To be honest if it is i don't even know why it is


    Posted from TSR Mobile
    Offline

    3
    ReputationRep:
    (Original post by Mehrdad jafari)
    For a rotating coil in a magnetic field:

    When the coil is vertical the flux linkage is greatest and when the coil is horizontal the induced emf is greatest

    I thought induced emf is the change of flux linkage so why when the coil is at right angle to the magnetic field lines the induced emf us zero? This sounds so unreasonable


    Posted from TSR Mobile
    The angle in question i believe is that between the field lines and the normal to the coil. When coil is vertical, angle = 0 therefore flux = max, when coil is horiz, angle = 90 flux =0
    Flux = BANcostheta
    Magnitude of emf = d/dt(N.flux)
    Offline

    2
    ReputationRep:
    (Original post by gcsestuff)
    Name:  ImageUploadedByStudent Room1433630613.964493.jpg
Views: 72
Size:  77.7 KB

    I'm struggling with this one too


    Posted from TSR Mobile
    I am guessing C.


    Posted from TSR Mobile
    Offline

    16
    ReputationRep:
    (Original post by Ilovemaths96)
    The angle in question i believe is that between the field lines and the normal to the coil. When coil is vertical, angle = 0 therefore flux = max, when coil is horiz, angle = 90 flux =0
    Flux = BANcostheta
    Magnitude of emf = d/dt(N.flux)
    Thanks for your response

    Yeah, mathematically that explains it but I'm having trouble with the idea that when the flux linkage is maximum the induced emf is zero


    Posted from TSR Mobile
    Offline

    16
    ReputationRep:
    (Original post by a.a.k)
    I am guessing C.


    Posted from TSR Mobile
    How do you assume that the collision is inelastic?


    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by Mehrdad jafari)
    How do you assume that the collision is inelastic?


    Posted from TSR Mobile
    Is the answer right.
    Btw i am assuming since they both moving together it cant inelastic otherwise they would be moving in opposite direction

    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by Mehrdad jafari)
    Thanks for your response

    Yeah, mathematically that explains it but I'm having trouble with the idea that when the flux linkage is maximum the induced emf is zero


    Posted from TSR Mobile
    I always relate it to how many lines cut through. Though i would suggest this as an exam answer

    Posted from TSR Mobile
    Offline

    16
    ReputationRep:
    (Original post by a.a.k)
    Is the answer right.
    Btw i am assuming since they both moving together it cant inelastic otherwise they would be moving in opposite direction

    Posted from TSR Mobile
    Your answer can't be right as the momentum is always conserved and can not change.
    And also not necessarily. Looking at the trucks one has a less mass than the other so during the interaction it might only exert such a force as to not move in the opposite direction to its original velocity


    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by Mehrdad jafari)
    Your answer can't be right as the momentum is always conserved and can not change.
    And also not necessarily. Looking at the trucks one has a less mass than the other so during the interaction it might only exert such a force as to not move in the opposite direction to its original velocity


    Posted from TSR Mobile
    And this is why is said i am guessing.

    Posted from TSR Mobile
    Offline

    16
    ReputationRep:
    (Original post by a.a.k)
    And this is why is said i am guessing.

    Posted from TSR Mobile
    It's cool man
    But guessing is not a good thing to do. We need to have confidence in our thinking. During my mocks i would never guess an answer to a question even though choosing an option would be of no harm as i wouldn't loose marks. So I would leave it blank. For me if i don't know, then i don't know


    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by Mehrdad jafari)
    It's cool man
    But guessing is not a good thing to do. We need to have confidence in our thinking. During my mocks i would never guess an answer to a question even though choosing an option would be of no harm as i wouldn't loose marks. So I would leave it blank. For me if i don't know, then i don't know


    Posted from TSR Mobile
    I do the same. But if i cant do them until the exam finishes then i just guess in the last minutes of the exam.

    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by Mehrdad jafari)
    It's cool man
    But guessing is not a good thing to do. We need to have confidence in our thinking. During my mocks i would never guess an answer to a question even though choosing an option would be of no harm as i wouldn't loose marks. So I would leave it blank. For me if i don't know, then i don't know


    Posted from TSR Mobile
    Whats the answer btw

    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    Answer is b to the momentum one.


    Posted from TSR Mobile
    Offline

    16
    ReputationRep:
    (Original post by a.a.k)
    I do the same. But if i cant do them until the exam finishes then i just guess in the last minutes of the exam.

    Posted from TSR Mobile
    That's true. If you guess you still have 25% chance of getting it right which is a good thing


    Posted from TSR Mobile
    Offline

    1
    ReputationRep:
    (Original post by a.a.k)
    I am guessing C.


    Posted from TSR Mobile
    I would say B: Clearly momentum doesn't change. For the kinetic energy, we know that the collision will slow down their overall speed (clearly they can't travel together at more than or equal to the speed of the first car!). But their mass is increased. kinetic energy is proportional to mv^2, where m gets bigger and v gets smaller, as we just showed. But v is squared, so v getting smaller causes more affect overall, so mv^2 get smaller overall. Hence the kinetic energy decreases. So: momentum is unchanged, kinetic energy decreases --> option B.
    Offline

    2
    ReputationRep:
    (Original post by gcsestuff)
    Answer is b to the momentum one.


    Posted from TSR Mobile
    Aww thnx i was nearly got it right

    Posted from TSR Mobile
    Offline

    16
    ReputationRep:
    (Original post by a.a.k)
    Aww thnx i was nearly got it right

    Posted from TSR Mobile
    Yeah c was just below b


    Posted from TSR Mobile
    Offline

    2
    ReputationRep:
    (Original post by Mehrdad jafari)
    Yeah c was just below b


    Posted from TSR Mobile
    And A was just above b :awesome:

    Posted from TSR Mobile
    Offline

    16
    ReputationRep:
    (Original post by gcsestuff)
    Answer is b to the momentum one.


    Posted from TSR Mobile
    I think i understand now why that it. Looking at the trucks, the moving one has a less mass than than the stationary one. This means that if the collision is perfectly elastic it would transfer some of its momentum( as it has a less mass)to the other truck, leaving itself with a lower velocity (in the opposite direction pehaps)so they couldn't have the same velocity after the collision.


    Posted from TSR Mobile
 
 
 
Poll
If you won £30,000, which of these would you spend it on?

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.