If dark nebulae are really dark, how do we know they are there?
What will be an ideal response?
In some cases, they are not thick enough to block all light, so allow some red light through. Even if dense enough, they can still be seen in profile against rich star fields that lie behind them in the plane of the Milky Way.
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A Boeing 737 airliner has a mass of 20 000 kg and the total area of both wings (top or bottom) is 100 m2 . What is the pressure difference between the top and bottom surface of each wing when the airplane is in flight at a constant altitude?
a. 1 960 N/m2 b. 3 920 N/m2 c. 7 840 N/m2 d. 4 560 N/m2 e. 3 070 N/m2
Imagine you throw a tennis ball vertically into the air. At the exact top of its trajectory it is at rest. What is the magnitude of its acceleration at this point?
A. 9.8 m/s2
B. –9.8 m/s2
C. 0 < 
< 9.8 m/s2
D. 0
E. Other (specify)
What happens to the atomic number (Z) and the mass number (A) when a nucleus emits an alpha particle?
a. Z increases by 1; A is unchanged. b. Z is unchanged; A is unchanged. c. Z decreases by 2; A decreases by 4. d. Z decreases by 1; A is unchanged.
An atom or chemical combination of atoms with a net electric charge is called a(n) ______________
Fill in the blank(s) with correct word