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homework1sol - Physics 20A Introduction to Astronomy...

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Physics 20A: Introduction to Astronomy Homework assignment #1 Solutions 1. Textbook, p. 20, question #6. Answer: (a) 4 . 642 × 10 3 ; 7 × 10 4 ; 3 . 47 × 10 1 . (b) 2 . 54 × 10 - 1 ; 4 . 6 × 10 - 3 ; 1 . 0243 × 10 - 1 . (c) 2 , 543 , 000; 200 . 43; 0 . 0007673. 2. Textbook, p. 20, question #8. Answer: (a) Find the time it would take to travel a distance of 4.2 AU, traveling at a constant speed of 20 km/sec. First, convert 4.2 AU into kilometers. 1 AU is equal to about 1 . 5 × 10 11 meters (rounding o± to 1 decimal place accuracy), which is equal to 1 . 5 × 10 8 kilometers. So, 4.2 AU is equal to 6 . 3 × 10 8 km. Then, using the fact that for travel at constant speed, (speed × time elapsed) = (distance travelled), we can divide the distance by the speed to obtain the time the asteroid takes for the journey, which is 3 . 15 × 10 7 seconds. Now: how long is that? Let’s compare it to one year. There are 60 seconds in a minute, 60 minutes in an hour, 24 hours in a day, and 365 days in a year. So the number of seconds in a year is 60 × 60 × 24 × 365, which is equal to 3 . 15 × 10 7 seconds. So, in the time it takes for the asteroid to reach the earth’s current position, the earth would go 1 complete orbit around the sun and return to its current position- so we might have to worry about a collision. (However, in reality the asteroid wouldn’t be traveling at a constant speed, and the chances of a collision would be very small.) 3. An electromagnetic wave has a frequency of 300 Megahertz. What is its wavelength?

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This note was uploaded on 04/16/2008 for the course PHYS 20A taught by Professor Staff during the Winter '02 term at UC Irvine.

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homework1sol - Physics 20A Introduction to Astronomy...

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