Which of the following factors in the simplified Drake equation is least well known?
A) Nhp, the number of habitable planets in our galaxy
B) fciv, fraction of life-bearing planets where intelligent civilizations have arisen at any time
C) fnow, fraction of civilization-bearing planets that have intelligent civilizations on them now
D) flife, fraction of life-bearing habitable planets
C
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Protostars are difficult to observe because
a. the protostar stage is very short. b. they are surrounded by cocoons of gas and dust. c. they radiate mainly in the infrared. d. the protostar stage is very short, they are surrounded by cocoons of gas and dust, and they radiate mainly in the infrared. e. they are all so far away that the light hasn't reached us yet.
A circular conducting loop lies in the xy plane of a certain reference frame. We are looking down on the loop with the +z axis pointing up at us. If the loop is immersed in a magnetic field that points in the -z direction and is increasing in magnitude as time passes, which way will current flow in the loop?
A. Counterclockwise B. Clockwise C. No current will flow.
The power of an engine is a measure of
A. the total amount of work it can perform. B. its volume. C. its ability to outperform a horse. D. the rate at which it can perform work.
An auto manufacturer advertises that their car can go "from zero to sixty in eight seconds." This is a description of what characteristic of the car's motion?
A) average speed B) instantaneous speed C) average acceleration D) instantaneous acceleration E) displacement