What is the approximate composition of the interstellar medium (by mass) in our region of the Milky Way?
A) 60% hydrogen, 40% helium
B) 70% hydrogen, 28% helium, 2% heavier elements
C) 70% hydrogen, 20% helium, 10% heavier elements
D) 50% hydrogen, 48% helium, 2% heavier elements
B) 70% hydrogen, 28% helium, 2% heavier elements
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A sound source of 100 watts radiates sound uniformly in all directions. The intensity of the sound at a distance of 4.00 m is
A. 0.301 
B. 0.353
C. 0.497
D. 0.535
E. 0.621
A common way a robotic spacecraft can be accelerated and have its trajectory changed without the use of any fuel is via
A) a gravitational slingshot from another spacecraft B) radiation pressure from the Sun C) the ejection of mass from the probe D) a gravitational slingshot from another planet
The average distance from Earth to the sun is defined as one astronomical unit (AU). If an asteroid orbits the sun in 1/3 of a year in a circular orbit, the asteroid's distance from the sun is closest to
A) 0.48 AU. B) 0.19 AU. C) 2.1 AU. D) 0.33 AU. E) 5.2 AU.