Two light beams of different frequency but the same intensity fall on a black (totally absorbing) surface, striking perpendicular to the surface. Which of the following statements are true? (There could be more than one correct choice.)
A) The light beams exert no pressure on the surface because light is just energy.
B) Both beams exert the same pressure on the surface.
C) Painting the surface white would not affect the pressure on it due to these beams.
D) If the surface were painted white (totally reflecting), the pressure on it would be less than when it was black.
E) The high-frequency beam exerts more pressure on the surface.
B
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Which of statement below about black holes is not true?
A) Although we are not 100% certain that black holes exist, we have strong observational evidence in favor of their existence. B) If you watch someone else fall into a black hole, you will never see him (or her) cross the event horizon; you'll only see him fade from view as the light he emits or reflects becomes more and more redshifted. C) A spaceship passing near a 10-solar-mass black hole is much more likely to be destroyed than a spaceship passing at the same distance from the center of a 10-solar-mass main-sequence star. D) If you fell into a black hole, you would experience time to be running normally as you plunged rapidly across the event horizon.
The two rigid objects shown in the figure below have the same mass, radius, and angular speed. If the same braking torque is applied to each, which takes longer to stop?
Earth doesn't experience a solar eclipse every month because
a. of unpredictable weather patterns. b. the Moon always keeps its same side toward the Earth. c. the Moon's orbit plane is not aligned with the Earth's orbit plane. d. its sometimes nighttime when the eclipse occurs. e. sometimes the Moon is too far away.
The primary evidence for an accelerating Universe comes from observations of young stars in the Milky Way.
A.) True, observations show that there were many more young, massive stars in the early Universe. B.) True, massive star supernovae allow us to measure the expansion rate of the Universe. C.) False, in order to measure accelerating expansion, we need to measure the distances of objects billions of light-years away. D.) False, evidence for an accelerating Universe comes from observations of the oldest stars in the Milky Way, white dwarfs. E.) False, we have to look at young stars in other galaxies beyond the Milky Way to measure the acceleration of the Universe.