Laboratory measurements show hydrogen produces a spectral line at a wavelength of 486.1 nanometers (nm). A particular star's spectrum shows the same hydrogen line at a wavelength of 486.0 nm. What can we conclude?
A) The star is moving toward us.
B) The star is moving away from us.
C) The star is getting hotter.
D) The star is getting colder.
A) The star is moving toward us.
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Einstein's theory of relativity tells us that travelers who make a high-speed trip to a distant star and back will
A) age more than people who stay behind on Earth. B) have more fun than people who stay behind on Earth. C) age less than people who stay behind on Earth. D) never be able to make the trip within their lifetimes.
A corner cube is formed by three plane mirrors perpendicular to one another resulting in a retroreflector. What is the angle between the directions of an incoming ray of light and of the corresponding outgoing ray of light for this device?
a. 90° c. 0° b. 180° d. 360°
Twenty kilometers is
a. 200,000 m. b. 20,000 m. c. 2,000 m. d. 200 m. e. 0.02 m.
The frictional force, due to air resistance, acting on an object is always
A. in the direction of the object's motion. B. in the upward direction. C. greater than the net force. D. smaller than object's weight. E. in the opposite direction to the object's motion.