Why do O stars exhibit weak hydrogen absorption lines?
A) At these high temperatures, nearly all the hydrogen is ionized, and is therefore unable to interact with light.
B) O stars are too cool to excite hydrogen atoms to the first energy level from which they can then absorb visible wavelengths of light.
C) O stars contain very little hydrogen.
A
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When an acid reacts with a carbonate or hydrogen carbonate, the products are water, carbon dioxide, and ______________
Fill in the blank(s) with correct word
A block slides on a rough horizontal surface from point A to point B. A force (magnitude P = 2.0 N) acts on the block between A and B, as shown. Points A and B are 1.5 m apart. If the kinetic energies of the block at A and B are 5.0 J and 4.0 J, respectively, how much work is done on the block by the force of friction as the block moves from A to B?
a.
?3.3 J
b.
+1.3 J
c.
+3.3 J
d.
?1.3 J
e.
+4.6 J
A Boeing-737 airliner has a mass of 30,000 kg. The total area of the wings is 100 m2 . What must be the pressure difference between the top and bottom of the wings to keep the airplane up?
a. 1960 Pa c. 7840 Pa b. 2940 Pa d. 15,700 Pa
One hundred milliliters of water is poured into a U-tube that has a cross-sectional area of 1 cm2. Then 100 milliliters of oil, with a density 80% that of water, is poured down one side of the U-tube so that the oil floats on the water. Find the difference in height of the liquid surfaces on the two sides of the U-tube.
What will be an ideal response?