Explorations: An Introduction to Astronomy (Arny), 7th Edition

Chapter 6: The Earth

Problems

1
Suppose the Earth's radius were only half of its real value. If the Earth's mass remained the same, what would be the average density? What if the Earth's mass were twice its real value, but the Earth's radius remained the same?
2
Using the periodic table in the back of the book, determine the astrophysical source(s) of the elements in the Earth's crust listed in table 6.1. Compare this source to the source of "precious" metals like gold, silver, and platinum.
3
What is the average density of an alloy made of 40% titanium, 30% iron, and 10% each of calcium, magnesium, and aluminum?
4
Seismic waves are partly reflected when they cross a boundary such as that between the mantle and the liquid core. Suppose that a P wave has a constant velocity of 8.0 km/sec. Suppose further that 700 seconds (about 12 minutes) after an earthquake near the surface, a seismometer detects a reflected P wave. How far below the surface is the liquid core–mantle boundary? Compare your answer to the distance in figure 6.7. Hint: Remember this is an echo.
5
The half-life of carbon 14, which is commonly used to date organic materials, is 5700 years. Make a graph of the percentage of original carbon present versus the age of a sample. What is the minimum age of a sample in which less than 13% of the original carbon 14 left? Less than 2%?
6
Studies of the South American and African plates indicate that for tens of millions of years they have spread apart at a roughly constant rate of approximately 4 centimeters per year. How many kilometers farther apart are the two continents now than they were 80 million years ago? How does this compare to 6000 kilometers, approximately the distance between some matching parts of the South American and African coastlines?
7
The total mass of the Earth's atmosphere is about 5.1 × 1018 kg. If you assume it is entirely made of nitrogen (N2) and oxygen (O2) gas molecules, what is the mass of oxygen gas in the atmosphere? The mass of one molecule of gas is equal to the sum of the masses of each atom (its atomic mass times 1.66 × 10-27 kg) in the molecule. Consult table 6.1 and the periodic table in the back of the book.
8
Use the principle of the Coriolis effect to draw a diagram to predict the air circulation flowing away from a "high-pressure system."
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