H I clouds can be observed using _____
a. optical telescopes above the earth's atmosphere
b. 21-cm radiation
c. x-ray radiation
d. infrared radiation
e. ultraviolet radiation
b
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The reaction energy associated with a nuclear reaction is
a. the total change in rest energy as a result of the reaction. b. equivalent to the disintegration energy. c. the minimum energy necessary for such a reaction to occur. d. called the threshold energy. e. the binding energy of the nucleons.
Two people, each of 70 kg mass, are riding in an elevator. One is standing on the floor. The other is hanging on a rope suspended from the ceiling. Compare the acceleration
of the first person to the acceleration 
of the second person. Which statement is correct?
a.
They are equal and opposite in direction.
b.
They are equal and have the same direction.
c.
The acceleration 
is greater than , but they have the same direction.
d.
The acceleration is greater than , but they have opposite directions.
e.
The acceleration >is less than , but they have the same direction.
Upon what data do measurements of sizes of eclipsing binaries depend?
A) their orbital periods and separations B) their masses and luminosities C) their Doppler shifts and durations of stages of their eclipses D) their temperatures and speeds E) their temperatures and masses
Suppose that a grandfather clock is calibrated correctly at sea level and is then brought up to the top of a tall mountain. What would need to be done to calibrate the clock at the top of the mountain?
1.Nothing, it should work fine since it was already calibrated at sea level. 2.The bob of the pendulum should be slid slightly down the rod. 3.The bob of the pendulum should be slid slightly up the rod. 4.It cannot be calibrated at the top of the mountain.