Astronomy II - Homework IV MCQs - Sproing 2008 | ASTR 1020, Assignments of Astronomy

Download Astronomy II - Homework IV MCQs - Sproing 2008 | ASTR 1020 and more Assignments Astronomy in PDF only on Docsity! Astronomy II (Astr 1020) Spring 2008 Prof Richard Ignace HOMEWORK #4 Notes: You will need a calculator, a pencil, and a standard scantron. Each question has one correct answer. Choose the best answer for each. Mark your answer on the scantron. This homework is due at the beginning of class on March 13. Late homeworks will not be accepted. 1. For a star that is 8 times more massive than the Sun, how will its expected Main Sequence lifetime compare to the Sun? a) About 8 times longer b) About 8 times shorter c) About the same d) About 64 times shorter e) About 64 times longer 2. Massive stars (say, greater than a solar mass) have more fuel to burn than stars like the Sun. Why, then, do they not live as long? a) They tend to have more heavy elements, and so they begin fusing Iron more rapidly. b) That’s not true. The more fuel a star has, the longer it will live. c) Since massive stars tend to form later, they form with proportionally less Hydrogen. d) Because of their higher core temperatures, they use up their fuel much more rapidly. 3. Why does the fusion of Iron in the core of a star signal the beginning of a supernova? a) Because when two iron atoms meet, they will fuse to form radioactive Uranium, effectively making the stellar core a giant fission bomb. b) Iron fusion releases a tremendous amount of energy, causing the star to blow itself apart. c) Iron is a catalyst, causing reactions to take place at an accelerated rate, resulting in an explosive release of energy. d) Because by this time the star is so hot, it can’t hold itself together. e) Iron fusion actually takes away energy from the core, causing it to collapse and then rebound, resulting in a supernova explosion. 1 4. Stars of all masses can burn a) iron. b) oxygen. c) carbon. d) helium. e) sodium. 5. Why do we say a solar-like star has run out of fuel after it has only used up about 10% of its total mass of Hydrogen? a) Because stars are only hot enough to fuse Hydrogen in the very center, a region that holds only about 10% of the star’s mass. b) Because it isn’t able to fuse anything heavier than Hydrogen. c) Because stars are only hot enough to fuse Hydrogen in the atmosphere, a region that holds only about 10% of the star’s mass. d) If a star released more than 10% of its total mass as energy, it would blow itself apart. 6. Consider a person with 100 kg of mass. If all of this were converted to energy via E = mc2, how long could a 100 Watt bulb be powered? (Use c = 3 × 108 m/s, then energy will be in Joules. Since Watts is Joules per second, your answer will be in seconds. Convert to years.) a) 2.9 billion years b) 9 × 1016 years c) 100 years d) 9 × 1018 years e) 29 million years 7. A planetary nebula is a) a nebula within which planets are forming b) produced by a supernova explosion c) a cloud of hot gas surrounding a planet d) the expelled outer envelope of a low mass star 8. The Sun has an equatorial rotation speed of about 2 km/sec, but many stars rotate much faster. If the Sun rotates once in 25 days, what is the rotation speed of a star of the same radius that rotates once in 15 hours? a) 3 km/s b) 30 km/s c) 80 km/s d) 2 km/s e) 12 km/s 2