A bullet train moving in the +x direction with x-velocity ? relative to the ground has lights on the roof of the head and tail cars that blink simultaneously in the train frame. The head car’s light happens to be passing by an observer on the ground just as it blinks. The observer sees the light from the tail car at a different time, but after correcting for the light travel time from the tail car, the observer concludes that in the ground frame
A. The tail car’s light blinked before the head car’s light.
B. The head car’s light blinked before the tail car’s light.
C. Both lights blinked simultaneously.
D. One cannot determine unambiguously which event occurs first in the ground frame.
A. The tail car’s light blinked before the head car’s light.
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Suppose you measure the density (mass per volume) of an object moving by you at high speed. How will its density compare to the density it would have at rest in your reference frame?
A) Its density would be higher. B) Its density would be lower. C) Its density would be the same. D) There is no way to know because relativity doesn't tell us anything about density.
A star's luminosity is the
A) total amount of energy that the star radiates each second. B) total amount of energy that the star will radiate over its entire lifetime. C) surface temperature of the star. D) lifetime of the star. E) apparent brightness of the star in our sky.
If Earth is closest to the Sun in January, why is much of the Northern Hemisphere cold in January?
A) It is cold because it is winter. B) The Southern Hemisphere is tilted away from the Sun in January. C) Solar energy favors the equatorial regions. D) The Northern Hemisphere is tilted away from the Sun in January.
What is the period of a satellite circling Mars 100 km above the planet's surface? The mass of Mars is 6.42 × 1023 kg, its radius is 3.40 × 106 m, and G = 6.67 × 10-11 m3/kg/s2
A) 1.75 hours B) 1.25 hours C) 1.15 hours D) 1.00 hours E) 1.45 hours