The ultimate speed of a solar-sail-propelled spacecraft is limited by the
A) low energy photons that the Sun produces
B) gravitational force of the Sun
C) fact that the intensity of sunlight falls off rapidly with distance
D) mass of the spacecraft
C
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A polarizer (with its preferred direction rotated 30° to the vertical) is placed in a beam of unpolarized light of intensity 1. After passing through the polarizer, the beam's intensity is
A) 0.2501. B) 0.7501. C) 0.5001. D) 0.8661. E) 0.5000.
This photo shows an object located in the halo of our Milky Way galaxy. Notice the many bright red dots in the photograph. What are they?
A) red giant stars B) cool, red main-sequence stars of spectral type M C) old white dwarf stars that have turned red in color D) massive supergiant stars E) starspots
What makes a star stop contracting?
A. The dust in it gets packed so tightly that it cannot continue to contract. B. Its gravity gets too strong for it to continue contracting. C. It gets hot enough that its pressure builds up, pushing back against the force of gravity. D. Its magnetic field pushes back against the force of gravity. E. It gets cool enough that it freezes, and the resulting ice is hard enough to push back against gravity.
The visible surface of the Sun is called the
a)chromosphere. b)photosphere. c)corona. d)celestial sphere. ?