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# NSAA Question on Nuclear Physics watch

1. 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
2. (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).
3. (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,

4. (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,

Ohhhh that makes loads more sence thank you so much!!!
5. (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 )
6. (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
7. (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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Updated: October 27, 2017
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