A-level Physics Blog: D at AS to an A in Year 13

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    CGP is definitely the way to go for the new spec, don't bother with any old spec resources. Best of luck
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    (Original post by jessyjellytot14)
    Yes! The CGP guide makes things much easier to understand than the textbook does in my opinion.
    Thank you, I've made all my AS notes so I think I'll just get the A2 book
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    (Original post by jessyjellytot14)
    11/09/16





    Attachment 579496


    If someone could tell me if my answer for this question is correct or not, that would be much appreciated

    I'm going to do one more question now and then try to relax.





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    I could not really figure out what is the power n in  7.3 \times 10^n . It seems like 7.
    The answer should be  7.3 \times 10^{-5} .
    Your working seems good.
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    (Original post by Eimmanuel)
    I could not really figure out what is the power n in  7.3 \times 10^n . It seems like 7.
    The answer should be  7.3 \times 10^{-5} .
    Your working seems good.
    Aaah yes I must have read the calculator wrong haha but thanks
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    12/09/16



    First day back at sixth form has been surprisingly good! I was expecting it to be terrible but I think year 13 is better than year 12 to be honest.
    I had double physics after lunch and we went over gravitational fields again because a lot of people in my class didn't turn up for the lessons when it was taught at the end of year 12 lol. Then we started learning about orbits and gravity and how to prove that v2 is directly proportional to r3.
    I'm actually feeling so much more motivated for physics after that lesson wooo.

    Before writing this post, I wrote up some neat notes on Orbits and Gravity using my revision guide. I'll add any extra information from my class notes to them tomorrow. I definitely think it's important to use a variety of sources for your knowledge- don't just rely on your teachers because they most likely will not tell you every single thing that you need to know. There's so much stuff in my revision guide that my teachers haven't mentioned so idk if we actually need to know it for the exam but i'm assuming that we do since it's in the revision guide. In addition, I would like to buy the A2 official AQA textbook but its like £30 and I don't have that much money atm ( I've already had to buy 2 maths textbooks, a psychology textbook, stationary supplies, not to mention the £24 I need for UCAS fml) so I might just get it in October half term or even for Christmas unless the physics department decide to buy them for us. The practice questions in it will be really useful because I don't trust the old spec papers lol.
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    13/09/16



    My lessons didn't start until 2pm today so I had all morning free to study. Ha. All I managed to get done was make notes on Scalars And Vectors (AS content) and answer the questions for it. In total, all of the questions made up 9 marks and I got 7/9 marks because I am actually hopeless at drawing scale diagrams. At least I now understand resolving forces better though.

    Mini rant alert Not really related to physics lol
    Spoiler:
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    I then went into the sixth form common room about an hour before my maths lesson started so I could review the topics we started last year, which I regretted because a group of guys in my year tried to make me and my friend feel and look bad for studying even though it was a 'study' period. They were just sat messing about, calling us year 12s because they haven't seen us before (Wish it could've stayed that way xx) and being general pr***s. Now I remember why I usually just study at home or in the library. At this point, I cannot stand being around people like that... lol I just need to get my grades and then I'll be over and out.
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    15/09/16


    I covered AS Forces yesterday which I definitely need more practice on and today I covered AS moments which I am actually quite good at.

    Today I had double maths in the morning and we started M1. I am so glad we are doing M1 this year because it should help with physics quite a bit (I hope) . We just did very simple suvat equations today.
    In the afternoon, I had an hour of physics and we did a circular motion recap. The boys in my class mess about so much, omg God help me.
    We got given a sheet to do for homework and I am stuck on one of the questions which I will post below. I just don't understand how you're supposed to get the answer or what equation you should use!...


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    (Original post by jessyjellytot14)
    15/09/16


    We got given a sheet to do for homework and I am stuck on one of the questions which I will post below. I just don't understand how you're supposed to get the answer or what equation you should use!...


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    In uniform circular motion,
     v = \omega r
     T =\frac{2 \pi }{\omega}

    Using the two relationships, the answer can be derived. Try it.
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    Good luck buddy!
    I'm redoing year 12 after the grades I got..
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    (Original post by jessyjellytot14)
    I'm doing maths and psychology which are going so much better than physics haha.
    And I do sort of have a revision timetable- I have a planner/bullet journal thing where I plan ahead my revision weekly which I find so much more useful than having the same revision schedule for the whole year because I can plan to do less things on the days when I'm busy/have things planned and as a result, its much easier to stick to.
    Funny, if you're doing the new Aqa spec for psychology we're doing the exact same exams and specs lol, managed a C in physics, revision was way too catered to the old spec causing me to do well in paper 1 then awful in paper 2, how were your maths and psychology grades?
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    (Original post by Mppcalc82)
    Funny, if you're doing the new Aqa spec for psychology we're doing the exact same exams and specs lol, managed a C in physics, revision was way too catered to the old spec causing me to do well in paper 1 then awful in paper 2, how were your maths and psychology grades?
    Yeah I'm doing AQA for psychology!
    And same... I don't know what I got in each of the physics papers but I wouldn't be surprised if I got an A/B in paper 1 and a U in paper 2 tbh.
    I got As in both maths and psychology.. the D in physics looks so out of place and dodgy lmao. I'm hoping that my physics teachers predict me a B though.
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    19/09/16


    I had double physics this afternoon and it was quite stressful tbh because when we did practice questions, I kept making stupid mistakes and getting them wrong. I'm going to read through my notes again soon to try and improve my understanding.
    I really wish I'd chosen to do further maths last year because that would make the mathematical side of physics seem a bit more straight forward. I also really like maths but for some reason, I'm crap at it in physics?? Tbh though, the only further maths modules that would help me are M2, M3 etc (I'm currently doing M1 in maths).

    After sixth form, I revised AS Velocity-Time Graphs and Acceleration-Time graphs, which I understand a lot better now. However, I'm confused about the Acceleration-Time Graphs because the part that shows "acceleration" is sloping downwards, and the acceleration is decreasing over time which should mean that the object is decelerating instead??
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    (Original post by jessyjellytot14)
    19/09/16



    After sixth form, I revised AS Velocity-Time Graphs and Acceleration-Time graphs, which I understand a lot better now. However, I'm confused about the Acceleration-Time Graphs because the part that shows "acceleration" is sloping downwards, and the acceleration is decreasing over time which should mean that the object is decelerating instead??
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    You may want to work out the velocity equation to convince yourself about your deduction. Non-constant acceleration motion is indeed pretty confusing.
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    Deceleration is a negative acceleration, not a reduction in acceleration.

    Deceleration is therefore a reduction in velocity (which is the intuitive bit).

    When I get confused about this, I think about driving a car. When the foot is on the accelerator, you accelerate. When the foot is on the brake, you decelerate. So that graph basically shows someone who starts off with their foot hard on the accelerator, then slowly lifting off, then slowing pushing harder on the brake. Basically, it's a drag racer. I find using real examples like this are helpful to figuring out what kind of motion a particular graph is representing.
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    (Original post by Eimmanuel)
    You may want to work out the velocity equation to convince yourself about your deduction. Non-constant acceleration motion is indeed pretty confusing.
    Yeah, I've noticed that the velocity increases as the acceleration decreases when you calculate a/t for certain points across the top half of the graph. Since the object's velocity is increasing but its acceleration is decreasing, would you assume that this is because the object is changing direction?

    (Original post by mik1a)
    Deceleration is a negative acceleration, not a reduction in acceleration.

    Deceleration is therefore a reduction in velocity (which is the intuitive bit).

    When I get confused about this, I think about driving a car. When the foot is on the accelerator, you accelerate. When the foot is on the brake, you decelerate. So that graph basically shows someone who starts off with their foot hard on the accelerator, then slowly lifting off, then slowing pushing harder on the brake. Basically, it's a drag racer. I find using real examples like this are helpful to figuring out what kind of motion a particular graph is representing.
    Aah okay thank you, that example helps me to understand it a bit better . Would a change in direction whilst at constant speed ever cause deceleration?
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    (Original post by jessyjellytot14)
    Yeah, I've noticed that the velocity increases as the acceleration decreases when you calculate a/t for certain points across the top half of the graph. Since the object's velocity is increasing but its acceleration is decreasing, would you assume that this is because the object is changing direction?
    One thing to bear in mind when an object changes direction, the velocity of the object needs to reach zero in order to change direction. But be careful, there is exception.

    In this case, the object is not changing but slow down. (I would avoid using deceleration or negative acceleration)

    If you integrate the acceleration equation with respect to time,

     a = 10 - 5t

     v = 10t - 2.5t^2 + C

    Assume C is zero, we obtain the graph below:
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    The change in direction occurs when t = 4.0 s not when acceleration is zero.

    When acceleration is zero, it implies either velocity is max or min.

    Assume C is -10 m/s, the graph of velocity is
    Attachment 581388581390

    Even the velocity is zero at t = 2.0 and when acceleration is zero, the object is not changing direction. This is the exception.

    Hope it helps.
    Attached Images
     
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    (Original post by jessyjellytot14)
    Aah okay thank you, that example helps me to understand it a bit better . Would a change in direction whilst at constant speed ever cause deceleration?
    This question is easiest to answer if I just take a moment to explain one important fact.

    Acceleration is a vector quantity, so it has a magnitude and a direction. Sometimes acceleration is quoted just as a number (e.g. 5 m/s^2), but there is always an implicit direction associated with that number (e.g. 5 m/s^2 Northwards).

    With you consider this fact, it should be clear that the sign of a quoted acceleration is completely dependent on the implicit direction of the acceleration. 5 m/s^2 acceleration Northwards is the same as -5 m/s^2 of acceleration Southwards. Exactly like taking 1 step forward when facing North lands you in the same place as taking 1 step backwards when facing South.

    Now, negative acceleration is commonly called deceleration. But the above paragraph shows how the sign of the acceleration only gives you part of the picture. An acceleration in one direction is the same as a deceleration in the other direction.

    So say a drag car accelerates Northwards from 0 to 60 mph. It then decelerates Northwards from 60 to 0 mph. That second part, the braking part, could equally be described as accelerating Southward from -60 mph to 0 mph, since it starts with a negative Southward velocity that then increases to 0. Flipping the reference direction (North/South) flips the sign of everything. But it all still works.

    To answer your question - whenever you change direction of travel, you are accelerating, even when at constant speed. You accelerate towards the direction you move towards. And, as described above, that is equivalent to a deceleration in the opposite direction. So yes, you can decelerate when changing direction at constant speed, but you just wouldn't normally phrase it in this way.
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    20/09/16



    Bad physics day lol. I had frees all morning so one of the things I did was answer some suvat questions from my revision guide and ended up making a few mistakes because I didn't know whether the acceleration was supposed to be positive or negative in some of the questions but I understand the concept better now thanks to Eimmanuel and mik1a .

    After sixth form, I intended on completing my physics homework which is to complete the booklet of past exam questions on Gravitational Fields but I've only done like a third of it because I don't have a clue what's going on... I've resorted to looking up the mark schemes for each question to see what you have to do. I really don't like doing this but at the same time, I don't want to hand in something to my teacher that will give me a crap grade because our UCAS predictions are being made in 10 days. It's not really cheating I suppose, because I'm just searching for guidance and I'm learning from it .
    I should probably resume to doing that now- I decided to make this post so I could have a break from it (physics makes me sad).
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    The sign is always a banana skin. My own trick, in an exam, is to draw a big arrow next to the diagram with a big "+" sign next to it to clearly show the direction that you're using as positive. Then anything that points the other way, you know it should have a negative sign. Saved me many, many marks.
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    (Original post by jessyjellytot14)
    20/09/16



    Bad physics day lol. I had frees all morning so one of the things I did was answer some suvat questions from my revision guide and ended up making a few mistakes because I didn't know whether the acceleration was supposed to be positive or negative in some of the questions but I understand the concept better now thanks to Eimmanuel and mik1a .

    After sixth form, I intended on completing my physics homework which is to complete the booklet of past exam questions on Gravitational Fields but I've only done like a third of it because I don't have a clue what's going on... I've resorted to looking up the mark schemes for each question to see what you have to do. I really don't like doing this but at the same time, I don't want to hand in something to my teacher that will give me a crap grade because our UCAS predictions are being made in 10 days. It's not really cheating I suppose, because I'm just searching for guidance and I'm learning from it .
    I should probably resume to doing that now- I decided to make this post so I could have a break from it (physics makes me sad).
    In regard to the sign issue, as mike had suggested a useful technique and I would add to his suggestion.
    In kinematics for one or two dimensional problems, it is arbitrary to choose which direction is positive as long as you are consistent. If you find it difficult to choose, then stick to the usual Cartesian coordinate (xy plane).
    You may want to post the question you have problems in deciding the direction.
 
 
 
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