Careful measurements reveal that a star maintains a steady apparent brightness at most times, except that at precise intervals of 93 hours. the star becomes dimmer for about 2 hours. The most likely explanation for this is that the star ________
a. has a very large "sunspot" on its surface
b. is a member of an eclipsing binary star system
c. is a white dwarf
d. is a Cepheid variable
e. is periodically ejecting gas into space, every 93 hours
b
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Uniform Circular Motion: When an object moves in uniform circular motion, the direction of its acceleration is
A. in the same direction as its velocity vector. B. in the opposite direction of its velocity vector. C. is directed toward the center of its circular path. D. is directed away from the center of its circular path. E. depends on the speed of the object.
Parallel Wires: Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in opposite directions,
A. one wire is lifted slightly while the other wire is forced downward against the table's surface. B. both wires are lifted slightly. C. the wires pull toward each other. D. the wires push away from each other.
One foolhardy day, a daring major (let's call him Tom) in the space force decides to become the first of his race to cross the event horizon of the black hole
To add to the drama, he decides to go in wearing only a thin space suit, which offers no shielding against radiation, no cushioning against any forces, and so on. Which of the following is most likely to kill him first (or at least cause significant damage)? (Hint: The key word here is first. Be sure to consider the distances from the black hole at which each of the noted effects is likely to become damaging.) A) the crush of gravity at the singularity embedded within the black hole B) the tidal forces due to the black hole C) the strong acceleration as he descends towards the black hole D) the X-rays from the accretion disk E) the sucking force from the black hole, which will cause his head to explode
For an electromagnetic wave in free space having an electric field of amplitude E and a magnetic field of amplitude B, the ratio of B/E is equal to
A) c B) c2 C) 1/c D) 1/c2 E)