Question: On problem 39, I don't understand how to get the mass given off per second because I don't know what the velocity (u) is of the radiation. Is there a formula that doesn't need the velocity known? I figured you need to use (gamma)mc^2 .

Answer: The energy comes from the sun as light. Thus it comes to us at the speed of light. However, I think you are misreading the problem. In the sun, mass is converted to energy via the reaction 4 H -> 1 He + 2 neutrinos + energy. The question is asking how much mass does 4x10^26 joules represent and then given that amount of mass, how long will the sun shine. My additional question was given the mass difference between the hydrogens and the helium, how long will the sun shine. (The difference in the two questions is that the book's question assumes that all of the mass in the sun is converted to energy. Mine assumes only the mass difference is converted to energy.)

Question: for 1-42 when you asked us to find the kinetic energy of each particle, not real sure how to go about doing that with these atoms, I was thinking I might have to use the 6.02x10^23 moles or something along those lines. Am I on the right track?

Is all of the remaining kinetic energy split evenly between the Radon atom and the alpha particle, or is there some relationship that the book does not mention?

Answer: You have to use energy and momentum conservation. The momenta are equal and opposite. The energies sum to the total energy. The kinetic energy is the total energy- mc^2.

Question: I'm pretty sure I found the energy and momentum, but I'm having trouble with the angle. Hope you can give me some insight on these.

Answer: From z-momentum conservation you get the "z-component" of the momentum. From x-momentum conservation you get that the magnitudes of the momenta are equal. From energy conservation and the fact that the momenta are equal you get that the energy of each particle is 1/2 the energy of the system. From E=pc you get the total momentum. You get the angle from cos(theta) = p_z/p_total.

Question: To find the momentum I thought that I could use the equation that you gave us which is r = qB/p, but what is the value of the charge (q)? Once I find that out, all of the other unknowns will be apparent.

Answer: For this part of the problem, you must convert everything to a consistent set of units. I would suggest MKS units. Then the charge would be in Coulombs, the field in Tesla, the momentum in kg m/sec and the radius in m.

Question: What is the value of "q" for the pion.

Answer: All "elementary" particles have charges that are integral multiples Of the electron's charge. Pions come in charges that are 1 e, 0 e, and -1 e. For this problem, the two pions have +/-1 e.