Answers to questions.

Question 1a on the homework: The baseline of the isosceles triangle is the distance between earth in the spring and earth in the fall, 1.5 x 10^8 m x 2.

1b. The power from the star is going everywhere! The power is "smeared" over a huge sphere. Guess what the radius of the sphere is? Hint: Did you get part I?) 

3a. In each fusion event in the sun 4 hydrogens are converted into helium. Look in the appendix on page A10 of the book FETU (the units there are atomic mass unit, each is 1.66 x 10^-27 kg). The mass of 4 hydrogens is LARGER than that of 1 helium. Where did the extra energy go? 

It went into energy!!! (That E=mc^2 thing.)

How many such fusion events can there be in the sun? We know the mass of 4 hydrogens. We know the mass of 80% of the sun. 

The number of events times the energy from each event will give you the available energy.