Problem Solving


1		Calculate the main-sequence lifetime of the Sun by first determining the rate at which it burns hydrogen (refer to chapter 5) and then dividing that rate into its core mass. If your answer is in seconds, convert to years, given that there are about 3.2 x 10⁷ seconds in a year.



2		Calculate the escape velocity from a red giant's atmosphere (use the formula for escape velocity from chapter 2). Assume that the star's mass is 1 M_sun and its radius is 100 R_sun How does this compare with the speed at which a planetary nebula shell is ejected?



3		How long will it take a planetary nebula shell moving at 20 kilometers per second to expand to a radius of one-fourth of a light year?



4		figure7.23 Figure 7.23 shows the H-R diagram of a star cluster. How old is it? (The dashed line is the position of the stars. The solid line is the main sequence.)



5		Calculate the average density of a red giant star in grams per cubic centimeter. Take the star's mass to be 2 x 10³ gm and its radius to be 3 x10¹² cm. How does this density compare with that of the air we breathe (about 10^-3 gm/cm³)?

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