Hey can anyone help explain these two questions for me? Edexcel physics unit 5 June 2012;
Question 5: Two distant stars are observed through a telescope. Star A is observed to be half as bright as star B. Star A is calculated to be twice as far away as star B.
Which of the following is correct?
A Star A has half the luminosity of star B.
B Star A has the same luminosity as star B.
C Star A has twice the luminosity of star B.
D Star A has 8 times the luminosity of star B.
Can anyone please explain how it is C using equations?
And the second question is-->
19)c)iv) Calculate the kinetic energy, in MeV, of the neutron released by the fusion of deuterium and tritium nuclei. Assume that the net momentum of the nuclei before fusion is zero.
You would have had to calculate that the energy released in the reaction (mass deficit) is 17.5 MeV but other than that, I have no idea! the mark scheme makes a weird assumption that Ek(alpha) + Ek(neutron) = 17.5?
Thank you, I appreciate this if you can explain these issues.