What do we mean by the singularity of a black hole?
A) It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.
B) It is the "point of no return" of the black hole; anything closer than this point will not be able to escape the gravitational force of the black hole.
C) It is the edge of the black hole, where one could leave the observable universe.
D) The term is intended to emphasize the fact that an object can become a black hole only once, and a black hole cannot evolve into anything else.
A) It is the center of the black hole, a place of infinite density where the known laws of physics cannot describe the conditions.
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Thanks to interferometry, a properly spaced set of 10-meter radio telescopes can achieve the angular resolution of a single, 100-kilometer radio telescope.
a. Yes, but with much lower sensitivity than a single, 100- kilometer telescope. b. Yes, and the resulting interferometer will have exactly the same properties as a single, 100-kilometer telescope. c. No, interferometry only works over much smaller distances. d. No, the blurring effects of Earth’s atmosphere limit the achievable angular resolution.
Which statement correctly locates the formation of the Earth and the appearance of the first humans on the cosmic calendar, which compresses the 14-billion year history of the universe into one "year," where "now" is exactly midnight,
A) Earth forms in January, life begins in April, and humans appear in early December. B) Earth forms in January, life begins in September, and humans appear in October. C) Earth forms in early September, life begins in late September, humans appear a few hours before midnight, Dec 31. D) Earth forms in early September, life begins in November, and humans appear on Dec 15.
The nuclear process having by-products with least radioactivity is
A) fission. B) fusion. C) about the same for both.
A 250-kg crate is placed on an adjustable inclined plane. If the crate slides down the incline with an acceleration of 0.25 m/s2 when the incline angle is 25°, then what should the incline angle be for the crate to slide down the plane at constant speed? Note: g = 9.8 m/s2
a. 12° c. 24° b. 21° d. 29°