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    On the 2016 Section 1 Paper

    When a stationary Uranium-238 nucleus decays by alpha emission it forms a nucleus of thorium-234. The total kinetic energy produced by the decay is E.
    What is the kinetic energy of the alpha particle?
    A. 4E/238
    B. 4E/234
    C. E/2
    D. 234E/238
    E. E

    I thought it was A because E=MC^2 so Mass and Energy are directly proportional, but the answer is D, which I kind of get because its lighter so would get more KE. Point is I don't know how I would go about doing one of these questions, can someone explain the logic plzzzz

    Also -- does anyone know what sort of marks cambridge are looking for on these papers? I know there meant to be hard to challenge applicants, but do they still want like >90%? Thanks x
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    (Original post by perks23)
    On the 2016 Section 1 Paper

    When a stationary Uranium-238 nucleus decays by alpha emission it forms a nucleus of thorium-234. The total kinetic energy produced by the decay is E.
    What is the kinetic energy of the alpha particle?
    A. 4E/238
    B. 4E/234
    C. E/2
    D. 234E/238
    E. E

    I thought it was A because E=MC^2 so Mass and Energy are directly proportional, but the answer is D, which I kind of get because its lighter so would get more KE. Point is I don't know how I would go about doing one of these questions, can someone explain the logic plzzzz

    Also -- does anyone know what sort of marks cambridge are looking for on these papers? I know there meant to be hard to challenge applicants, but do they still want like >90%? Thanks x
    I can't help with the question because I also found it difficult and got it wrong.

    However I wanted to say that Cambridge definitely aren't looking for you to get >90%!! Around 50% is considered a competitive score on the MCQs, so don't worry about it too much (also, the NSAA isn't the be all and end all of your application).
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    (Original post by perks23)
    On the 2016 Section 1 Paper

    When a stationary Uranium-238 nucleus decays by alpha emission it forms a nucleus of thorium-234. The total kinetic energy produced by the decay is E.
    What is the kinetic energy of the alpha particle?
    A. 4E/238
    B. 4E/234
    C. E/2
    D. 234E/238
    E. E

    I thought it was A because E=MC^2 so Mass and Energy are directly proportional, but the answer is D, which I kind of get because its lighter so would get more KE. Point is I don't know how I would go about doing one of these questions, can someone explain the logic plzzzz

    Also -- does anyone know what sort of marks cambridge are looking for on these papers? I know there meant to be hard to challenge applicants, but do they still want like >90%? Thanks x
    E=mc^2 is about interconversion of mass and energy, which we don't really see about here.

    This is more about collision/explosion mechanics.

    Spoiler:
    Show


    Assuming a zero momentum frame, p_{234} = p_4

    E=\frac{1}{2}mv^2 \Rightarrow E=\dfrac{p^2}{2m}

    E_4 = \dfrac{(p_4)^2}{4}

    E = \dfrac{(p_4)^2}{4} + \dfrac{(p_{234})^2}{234} = \dfrac{(p_4)^2}{4}+\dfrac{(p_4)^  2}{234}

    \Rightarrow E= \dfrac{(p_4)^2}{4} \left[ 1 + \dfrac{4}{234} \right]

    \Rightarrow E=E_4 \dfrac{234+4}{234}

    \Rightarrow E_4 = \dfrac{234}{238}E





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    (Original post by K-Man_PhysCheM)
    E=mc^2 is about interconversion of mass and energy, which we don't really see about here.

    This is more about collision/explosion mechanics.

    Spoiler:
    Show



    Assuming a zero momentum frame, p_{234} = p_4

    E=\frac{1}{2}mv^2 \Rightarrow E=\dfrac{p^2}{2m}

    E_4 = \dfrac{(p_4)^2}{4}

    E = \dfrac{(p_4)^2}{4} + \dfrac{(p_{234})^2}{234} = \dfrac{(p_4)^2}{4}+\dfrac{(p_4)^  2}{234}

    \Rightarrow E= \dfrac{(p_4)^2}{4} \left[ 1 + \dfrac{4}{234} \right]

    \Rightarrow E=E_4 \dfrac{234+4}{234}

    \Rightarrow E_4 = \dfrac{234}{238}E






    Ohhhh that makes loads more sence thank you so much!!!
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    (Original post by Franki108)
    I can't help with the question because I also found it difficult and got it wrong.

    However I wanted to say that Cambridge definitely aren't looking for you to get >90%!! Around 50% is considered a competitive score on the MCQs, so don't worry about it too much (also, the NSAA isn't the be all and end all of your application).
    Oh really?!! That’s great thanks )
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    (Original post by perks23)
    On the 2016 Section 1 Paper

    When a stationary Uranium-238 nucleus decays by alpha emission it forms a nucleus of thorium-234. The total kinetic energy produced by the decay is E.
    What is the kinetic energy of the alpha particle?
    A. 4E/238
    B. 4E/234
    C. E/2
    D. 234E/238
    E. E

    I thought it was A because E=MC^2 so Mass and Energy are directly proportional, but the answer is D, which I kind of get because its lighter so would get more KE. Point is I don't know how I would go about doing one of these questions, can someone explain the logic plzzzz

    Also -- does anyone know what sort of marks cambridge are looking for on these papers? I know there meant to be hard to challenge applicants, but do they still want like >90%? Thanks x
    I thought it was A too, please explain if you find out why it's D
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    (Original post by G.Y)
    I thought it was A too, please explain if you find out why it's D
    K-Man_PhysCheM gave a really good explanation, see above! — just turn it into a momentum question 👍🏼😊
 
 
 
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