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The Proof is Trivial physics edition? Watch

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    What do you guys think about having a thread, such as 'The Proof is Trivial' in the physics section to spice it up?
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    Not sure that A level physics lends itself well at all to that sort of game. I'm not good enough at maths to understand WTH is going on in that thread... if you post an example problem then maybe I'll change my mind.
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    Physics is not about proof. Physics is about using mathematics to model certain scenarios that play out in the real world. So the name would not be appropriate. Maybe a name like "problem solving for Physics".
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    (Original post by Blutooth)
    Physics is not about proof. Physics is about using mathematics to model certain scenarios that play out in the real world. So the name would not be appropriate. Maybe a name like "problem solving for Physics".
    I was purely suggesting to have a thread similar to that of TPIS, I imagine it to just be a collection of hard problems to have a crack at, the name of course is debatable.

    Also, given a certain physics based question, of course a proof can be derived, I'm not aiming for it to be abstract theoretical problems. QED questions etc.
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    I like the idea of having a hard physics questions thread. Still not too sure on the types of questions we could do though, the obvious examples I can think of are just complicated versions of boring problems... give us an example please!
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    Try this one

    A block of mass 8 kg is resting on a slope of 30° to the horizontal. A force of 80 N is applied up the slope at an angle of 20° relative to the slope. Given the coefficient of kinetic friction is 0.5, what is the acceleration of the block up the slope?
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    (Original post by langlitz)
    Try this one

    A block of mass 8 kg is resting on a slope of 30° to the horizontal. A force of 80 N is applied up the slope at an angle of 20° relative to the slope. Given the coefficient of kinetic friction is 0.5, what is the acceleration of the block up the slope?
    Too easy, it's basically an M1 question. The point would be to make questions that are a bit harder but rely on the same knowledge base. Regardless, I got 0.253ms-2? Up the slope.

    It would be nice to have some more conceptual questions TBH but until I think of something:

    Describe qualitatively what would happen if the 80N force was replaced by a 50N force acting at 500 to the inclined plane.
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    (Original post by lerjj)
    Too easy, it's basically an M1 question. The point would be to make questions that are a bit harder but rely on the same knowledge base. Regardless, I got 0.253ms-2? Up the slope.

    It would be nice to have some more conceptual questions TBH but until I think of something:

    Describe qualitatively what would happen if the 80N force was replaced by a 50N force acting at 500 to the inclined plane.
    Actually that's not the answer Try again

    I would say qualitatively, without any calculations, that the block would remain stationary on the slope


    Out of interest are you doing A level or are you a physics student?

    EDIT:
    This question requires a bit more thought than appears at first glance
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    (Original post by lerjj)
    Too easy, it's basically an M1 question. The point would be to make questions that are a bit harder but rely on the same knowledge base. Regardless, I got 0.253ms-2? Up the slope.
    Where is your working? God knows how you got there
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    (Original post by Phichi)
    Where is your working? God knows how you got there
    It's a clone of an M1 question. Although since it's wrong I'll do it properly of course.
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    (Original post by langlitz)
    Actually that's not the answer Try again

    I would say qualitatively, without any calculations, that the block would remain stationary on the slope


    Out of interest are you doing A level or are you a physics student?

    EDIT:
    This question requires a bit more thought than appears at first glance
    Woops, did that too fast. Actual working should have looked like this:
    Resolving perpendicular: N=8gcos(30)-80sin(20)
    Resolving parallel: F_r=80cos(20)-8gsin(30)-0.5N

    Which gives 1.96ms-2 after F=ma.

    I still think that's too easy, and I'm doing A level.
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    (Original post by lerjj)
    Woops, did that too fast. Actual working should have looked like this:
    Resolving perpendicular: N=8gcos(30)-80sin(20)
    Resolving parallel: F_r=80cos(20)-8gsin(30)-0.5N

    Which gives 1.96ms-2 after F=ma.

    I still think that's too easy, and I'm doing A level.
    Still wrong... answer is 1.78 ms-2
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    (Original post by langlitz)
    Still wrong... answer is 1.78 ms-2
    You sure? What value of g are you using?
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    (Original post by lerjj)
    You sure? What value of g are you using?
    Oh right, I'm guessing you're using g= 9.81?
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    (Original post by langlitz)
    Oh right, I'm guessing you're using g= 9.81?
    Protip: use g instead of 10 or 9.81. Then in your final answer, give f(g) \approx f(9.81) or whatever.
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    Name:  ImageUploadedByStudent Room1420031674.141527.jpg
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    Should be a theta on the diagram below the applied force vector arrow
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    (Original post by langlitz)
    Oh right, I'm guessing you're using g= 9.81?
    I used 9.8 because that's what we use in M1 I've just checked all three and you get your answer for g=10, 1.96 for g=9.8 and 1.95 for g=9.81.
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    (Original post by lerjj)
    I used 9.8 because that's what we use in M1 I've just checked all three and you get your answer for g=10, 1.96 for g=9.8 and 1.95 for g=9.81.
    I have no idea what M1 is but yeah sorry your solution is correct
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    (Original post by Smaug123)
    Protip: use g instead of 10 or 9.81. Then in your final answer, give f(g) \approx f(9.81) or whatever.
    This was a rather number-y question. a=10(cos(20)+\mu sin(20)-g(sin(30)+\mu cos(30)) didn't really seem right.
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    (Original post by lerjj)
    This was a rather number-y question. a=10(cos(20)+\mu sin(20)-g(sin(30)+\mu cos(30)) didn't really seem right.
    Protip: don't put any numbers in until you have you're final equation in the form you need
 
 
 
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