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
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.
A lithium-sodium
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