ASTR 1010 – Spring 2016 – Prof. Magnani
Answer Key – Homework 1
Question 1 – Ch. 1; #28
The information would reach us at the speed of light which covers the distance
between the Earth and the Sun in a bit more than eight minutes. Use the formula
d=vt, with the distance being 1.5 x 108 km, and the speed of light being 3.0 x 105
km/s.
Question 2 – Ch. 1; #29
The Andromeda Galaxy is about two and a half million light-years away, so it would
take about two and a half million years for that information to reach us. This
problem is like question 28. To make it easy, you can take the speed of light to be 1
light-year per year.
Question 3 – Ch. 1; #33
In common, everyday language, the word theory is reserved for a type of guess
about how things work that is not based on any substantial set of facts or
observations. In this sense, the word is used in a dismissive or even pejorative
sense. In contrast, scientists reserve the term theory for a well-developed and
thoroughly tested set of ideas about how nature works.
Question 4 – Ch. 1; #34
In common, everyday language, the words theory and hypothesis both tend to have
the same meaning; namely, a type of guess not based on any substantial set of facts
or observations. Scientists reserve the term hypothesis for an educated guess or
hunch about the way nature works, and reserve the term theory for those
hypotheses that have been thoroughly vetted by numerous experiments and
consistency checks – usually requiring years or even decades of work.
Question 5 – Ch. 1; #36
Some scientific “facts” are not set in stone, but are liable to change as new data or
observations reveal new information. In that sense, science is free to change and is
not as absolute as other disciplines. Note that I said “some” scientific facts. Not
everything is mutable or subject to new interpretation.
Question 6 – Ch. 1; #41
a) 7.0 x 109
b) 3.46 x 10-3
c) 1.238 x 103
Question 7 – Ch. 1; #42
a) 534,000,000
b) 4100
c) 0.0000624
Question 8 – Ch. 1; #44
a)
b)
c)
d)
22 = 4; so 4 times bigger
32 = 9; so 9 times bigger
(1/2)2 = ¼; so it’s one quarter the size
(1/3)2 = 1/9; so it’s one ninth the size
Question 9 – Ch. 1; #45
This is like the first two problems…Use d = vt and get 384,000/800 = 480 hours or
20 days.
Question 10 – Ch. 1; #48
Surface area goes as the radius squared, thus the surface area of the moon is (1/4)2
or 1/16 that of the Earth.
Question 11 – Ch. 1; #53
The key concept here is area. While the 18-inch pizza is twice the diameter of the 9inch pizza, it is 4 times the area (remember area of a circle is pi times the radius
SQUARED). So the 18-inch pizza is twice the price but it gives you 4 times as much
pizza!
Question 12 – Ch. 1; #55
Use dimensional analysis (using units as numbers) to help you out:
4 [dollars/gallons]
x 1/3.8 [1/ liters/gallon] =
4 [dollars/gallons]
x 1/3.8 [gallons/liter] =
4/3.8 [dollars/liter] = 1.05 dollars/liter