What are the two most important intrinsic properties used to classify stars?
A) Mass and age
B) Luminosity and surface temperature
C) Distance and luminosity
D) Distance and surface temperature
E) Distance and color
B
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Briefly explain the purpose of the equation Number of Civilizations = Np × flife × fcivilization × fnow
What will be an ideal response?
The block shown is pulled across the horizontal surface at a constant speed by the force shown. If M = 5.0 kg, F = 14 N and ? = 35°, what is the coefficient of kinetic friction between the block and the horizontal surface?
A. 0.44 B. 0.33 C. 0.38 D. 0.28 E. 0.17
Which of the following best describes why the Sun emits most of its energy in the form of visible light?
A) Nuclear fusion in the Sun's core produces visible light photons. B) The Sun's gas is on fire like flames from wood or coal, and these flames emit visible light. C) Like all objects, the Sun emits thermal radiation with a spectrum that depends on its temperature, and the Sun's surface temperature is just right for emitting mostly visible light. D) The visible light comes from energy level transitions as electrons in the Sun's hydrogen atoms jump between level 1 and level 2.
A charge of 50-?C is placed on the y axis at y = 3.0 cm and a 77-?C charge is placed on the x axis at x = 4.0 cm. If both charges are held fixed, what is the magnitude of the initial acceleration of an electron released from rest at the origin?
a. 1.2 × 10^20 m/s2 b. 1.5 × 10^20 m/s2 c. 1.0 × 10^20 m/s2 d. 1.8 × 10^20 m/s2 e. 2.0 × 10^20 m/s2