Astro 1050     HW#3 Solutions
Question 1.  While all of the following are discoveries of Galileo, which of the four listed is NOT one which DIRECTLY contradicts the "Aristotelian" view of the heavens.
a.The discovery of "imperfections" on celestial bodies, such as mountains and valleys on the moon and changing sunspots on the sun.
b.The discovery of the phases of Venus, ranging from new to crescent to "quarter" to gibbous to full.
c.The discovery that the Milky Way is actually composed of a large number of very faint stars.
d.The discovery of four moons orbiting Jupiter.

Homework #3 solutions
Question 2   Imagine that you're kidnapped by aliens and transported to a distant world in a different solar system. They will release you if you show your understanding of orbital dynamics. There is a planet with a period (year) 8 times longer than the planet you are on. How much further away is it from the local sun?
 
a.2 times as far.   b.4 times as far.   c.8 times as far.   d.16 times as far.   e.32 times as far.
Key is to use KEPLER’S 3rd Law, period squared equals radius cubed.  R = period2/3 = 82/3 = 4

Homework #3 solutions
Question 3   Newton concluded that some force had to act on the moon because
 
a.the moon moved at a constant velocity.
b.a force is needed to pull the moon outward.
c.a force is needed to pull the moon away from straight-line motion.
d.a force is needed to keep the moon in motion.
e.all of the above.

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Question 4   (1 point) What is the circular velocity of Mercury? You will need values from Appendix A of the textbook. You might also find the example in By the Numbers 4-1.
 
a. About 5 km/s.
b. About 25 km/s.
c. About 50 km/s.
d. About 75 km/s.
e.About 100 km/s.
Start From Vc = (GM/R)0.5
G = 6.67x10-11 m3/kg s2, M=2x1030 kg, R=5.8x107 km

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 Question 5   (1 point) If a space probe were sent into an orbit around the sun that brought it as close as 0.5 AU to the sun and as far away as 5.5 AU, what would be its orbital period?
 
a.1.0 years b. 2.5 years c. 4.1 years d. 5.2 years
Use Kepler’s third law: P2 = a3 for both these problems.  Use units of years and AUs to make life simple.  Use elliptical geometry to solve for a.  I’ll work this in review session.

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Question 6  Tycho Brahe's greatest contribution to astronomy was
 
a.his 20 years of careful observations of planetary positions.
b.his model of the universe.
c.his telescopic observations of the moon.
d.his discovery of three laws of motion

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Question 7   (1 point) What is the correct order that shows increasing photon energy for wavebands of the electro-magnetic spectrum?
 
a.Radio -- Infrared -- Optical -- Ultraviolet -- X-ray -- Gamma Ray
b.X-ray -- Gamma Ray -- Radio -- Infrared -- Optical -- Ultraviolet
c.Infrared -- Radio -- Optical -- Ultraviolet -- Gamma ray -- X-ray
d.Radio -- Optical -- Infrared -- Ultraviolet -- X-ray -- Gamma Ray
e.Infrared -- Radio -- Ultraviolet -- X-ray -- Optical -- Gamma Rays

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Question 8.  Of the following types of electromagnetic radiation, which has the lowest energy per photon?
 
a.gamma-rays
b.radio – lowest frequency, longest wavelength, lowest E
c.infrared radiation
d.visible light
e.x-rays
Question 9   (1 point)Compared to gamma rays, radio waves travel
 
a.slower (i.e., at the speed of sound).
b.At the same speed. !!!!!!!!!!!!!!!!!!  Both are light!
 c.faster.

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Question 10:   The thickness of a plastic freezer storage bag is roughly 0.1 mm. How many wavelengths of red light is this?
Simple math and conversion.  mm is 1/1000 m, nm is 10-9 meter.
0.1mm/700 nm = 140.