Which emits radiation of the highest frequency?
A) a red-hot star
B) the Sun
C) a blue-hot star
D) all the same
Answer: C
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Calculations show that gravity begins to overcome thermal pressure in clouds that are
A) less massive than the Sun. B) more massive than the Sun. C) more massive than ten times the Sun. D) more massive than a hundred times the Sun. E) more massive than a thousand times the Sun.
One hypothesis suggested to explain the uniform age of the surface of Venus is that
a. Venus's surface is 4 billion years old and has not been affected by flooding or slow evolution. b. Venus's surface is made of rocks that are much harder than Earth's and thus last longer. c. Venus periodically goes through a catastrophic melting of its entire surface. d. Venus's clouds protect it from meteorites so that very few impacts occur to change its surface. e. dust storms deposit large amount of dust on the surface, making it appear of uniform age.
We expect neutron stars to spin rapidly because they conserve angular momentum
a. True b. False Indicate whether the statement is true or false
Two twin sisters, Gwen and Jackie, are both 20 years old in the year 2050. Suppose that Jackie makes the round-trip to Vega, which is 25 light-years away, at an average speed of 0.9999c. Which of the following correctly describes the situation when Jackie returns to Earth? (Ages in this problem refer to biological ages, that is, how much time has passed for each sister since she was born.)
A) It's the year 2100. Gwen (who stayed home) is 70 years old, but Jackie is only a little older than her age of 20 when she left. B) It's the year 2100 and both twin sisters are 70 years old. C) It's the year 2100. Gwen is 70 years old. Jackie is 19. D) According to Gwen, Jackie returns to Earth in the year 2100, but according to Jackie, she returns in the year 2051.