AL Physics 8182

2009-03-01 6:47 pm

81
A stationary radioactive nucleus of mass N units emits an alpha particle of mass 4 units, leavinga residual nucleus of mass(N-4)units. The radio of the KE of the alpha particle to the KE of the residual nucleus is?

82
A radioactive source with a half-life T initally contains N atoms of the radioactive element. The energy released in each disintegration is E. What is the total energy released in time 2T?

回答 (1)

Prof. Physics

2009-03-01 7:26 pm

✔ 最佳答案

81. Let u and v be the velocity of the alpha particle and the residual nucleus after the decay respectively.

By the law of conservation of momentum

0 = 4u + (N - 4)v

u = [(4 - N)/4]v ... (1)

So, ratio of K.E. of the alpha particle to that of the residual nucleus

= 1/2 (4)u^2 : 1/2 (N - 4)v^2

= 4[(4 - N)v/4]^2 : (N - 4)v^2

= (N - 4) / 4 : 1

= (N - 4) : 4

This is 81 AL physics mc Q.33. The answer is A.

82. After half-life T, number of decayed atoms = N / 2

And the corresponding energy released is NE / 2

Therefore, after 2T, number of decayed atoms = 3N / 4

So, the total energy released

= (NE / 2) X (3N / 4)/(N / 2)

= 3NE / 4

This is 82 AL physics mc Q.35. The answer is C.

參考: Physics king

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