# Physics Questions

## Question

1.) The Luminosity of a star depends on two quantities, its radius and its temperature; 𝐿~𝑅²T⁴

a.) If you double the radius of the star how will this affect the luminosity of the star?
b.) If you double the temperature of the star, how will this affect the luminosity of the star?
c.) If you make the radius 9 times larger, and cut the temperature by 3, how will this affect the luminosity of the star?
d.) What quantity, radius or temperature, has a bigger effect on the luminosity of a star? Why?

2.) You look at the sky at night, and notice three stars. Star A has an apparent magnitude of 5.2, Star B has an apparent magnitude of 6.4, and Star C has an apparently magnitude of 1.2
a.) Which star appears brightest?
b.) Are you able to determine which of these stars actually IS brighter? If not, what additional information would you need to determine this?
c.) Suppose you are told that all three stars have an absolute magnitude of 5.2. For each star, state whether they are closer than 10 parsecs away, farther than 10 parsecs away, or exactly 10 parsecs away.
d.) How much brighter does Star C appear than Star B?

3.) Below, you are told two of the force, mass, or acceleration. Find the one that is missing. Show your work!
a.) m=3kg, a=20m/s². F=?
b.) m=2kg, a=30m/s². F=?
c.) F=60N, m=10kg. a=?
d.) F=60N, a=15m/s². m=?
e.) In each of these, you should have found that all of them had the same force; F=60N. Why did they not all have the acceleration? If the same force acts on two different objects, will the objects respond the same way?

4.) The Sun’s gravity acts on the Earth, compelling it to orbit. As the Earth orbits, its speed stays relatively constant
a.) If a force causes an acceleration, and the Earth’s speed isn’t changing, how can gravity be acting on the Earth.
b.) How does the force of gravity of the Sun acting on the Earth compare to the force of gravity of the Earth acting on the Sun?
c.) Based on b.), How does the acceleration of the Earth compare to the acceleration of the Sun?

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