The number of stars in the observable universe
A) is approximately equal to the population of the Earth at the turn of the 21st century
B) cannot be estimated
C) is approximately equal to the total number of sand grains on every beach on Earth
D) is infinitely large
C
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You are in an airplane, traveling relative to the ground at 500 km/hr. You throw a baseball toward the front of the plane at a speed of 50 km/hr. How fast would someone on the ground say the baseball is moving?
A) 550 km/hr B) 50 km/hr C) 500 km/hr D) 450 km/hr.
Cosmic inflation caused the universe to expand, for a brief period, at faster than lightspeed. But special relativity says that nothing can move faster than lightspeed. How can this contradiction be resolved?
A) The laws of physics (conservation of energy, special relativity, etc.) as we presently know them were not valid during the "inflationary period" that existed for a fraction of a second into the big bang. B) We now realize that special relativity does not apply to dark energy. C) Special relativity says nothing can move through space at faster than lightspeed, but doesn't restrict the speed at which space can expand. D) It hasn't yet been resolved, but scientists are working on resolving it. E) The laws of specially relativity were not valid during the inflationary period, but the other laws (such as conservation of energy) were valid.
A hydrogen atom is in the 6h state. Determine the principal quantum number
A) 0 B) 3 C) 5 D) 6 E) 7
When an atom has an electron removed, then its net charge is
A. negative. B. unchanged. C. positive. D. It is impossible to remove an electron from an atom