The main practical problem associated with building an interstellar ramjet is
A) making the ship large enough to scoop up enough hydrogen fuel given that the density of hydrogen in space is so low
B) producing enough thrust to accelerate the spacecraft to a high enough speed
C) separating the matter and antimatter fuels from each other
D) receiving enough photon energy to propel the craft
A
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Resolution: Even with perfect optics, what is the resolution limit (in radians) of the Hubble Space Telescope when it is focusing light of wavelength 400 nm? The mirror diameter is 2.4 m.
Fill in the blank(s) with the appropriate word(s).
Each Voyager spacecraft carries a "postcard" designed to be understandable to any aliens that might someday encounter it. On the "postcard," scientists pinpointed the location of Earth by triangulating it between pulsars. Why did the scientists choose pulsars rather than some other type of star?
A) Pulsars are easy to identify by their almost perfectly steady periods of pulsation. B) Pulsars are very bright and therefore easy to find. C) Several pulsars are located within a dozen light-years of our solar system, making them useful for finding our solar system. D) We're pretty sure that aliens will have only radio telescopes and not optical telescopes, so they'll have a better chance of seeing pulsars than ordinary stars.
Which publication was Kepler's masterpiece, providing strong evidence to planetary motion and a heliocentric Universe?
a. Alfonsine Tables b. De Revolutionibus c. Rudolphine Tables d. The Prutenic Tables e. Sidereus Nuncius
Power: A sand mover at a quarry lifts 2000 kg of sand per minute a vertical distance of 12 m. The sand is initially at rest and is discharged at the top of the sand mover with speed 5.0 m/s into a loading chute. What minimum power must be supplied to this machine?
A. 520 W B. 3.9 kW C. 6.7 kW D. 4.3 kW E. 1.1 kW