Download Astronomy Assignment #5: Newton`s Law of Gravity

Astronomy Assignment #5: Newton's Law of Gravity
Your Name______________________________________
Your Class Meeting Time __________________________
This assignment is due on Monday, 17 Feb 2014
Submit this cover sheet with your assignment.
Complete the assigned problems from the text listed below and address the Instructor Assigned Topic.
Mathematical problems may be hand written. Write out the problem, show your work in solving the
problem and state your answer in a complete sentence. Failure to complete all three of these tasks will
result in less than full credit awarded.
Answer the following Review Questions from Nick Strobel’s AstronomyNotes: Chapter 5: Newton's Law
of Gravity
Review Questions
1. What basic fundamental assumption did Newton make about the laws of nature on the
Earth and in space?
2. What things does gravity depend on?
3. How does gravity vary with distance between objects and with respect to what do you
measure the distances?
4. What would happen to the Earth's orbit if the Sun suddenly turned into a black hole
(of the same mass)? Why?
5. What important laws of planet motion can be derived from Newton's law of gravity?
6. What is the difference between mass and weight?
7. If Joe Astronaut has a mass of 40 kilograms on the Earth, how much mass would he
have on an asteroid with 10 times less surface gravity than the Earth's surface
gravity? Explain your answer.
8. Why is gravity called an ``inverse square law''?
9. What is the difference between a simple inverse relation and an inverse square
relation?
10. If the Earth was 3 A.U. from the Sun (instead of 1 A.U.), would the gravity force
between the Earth and the Sun be less or more than it is now? By how many times?
11. If Mercury was 0.2 A.U. from the Sun (instead of 0.4 A.U.), would the gravity force
between Mercury and the Sun be less or more than it is now? By how many times?
12. Why do astronauts in orbit around the Earth feel ``weightless'' even though the Earth's
gravity is still very much present?
13. What keeps satellites orbiting the Earth moving along their curved paths?
14. What two things must be determined first in order to calculate the mass of a planet or
a star?
15. Jupiter's moon Io has about the same mass as the Moon and orbits Jupiter at about the
same distance that the Moon orbits the Earth (center to center). Then why does Io
take only 1.8 days to orbit Jupiter but our Moon takes 27.3 days to orbit the Earth?
16. Astronomers were able to accurately measure the orbital periods of the moons of
Jupiter since the time of Galileo, so why was an accurate value for Jupiter's mass not
found for over 300 years until the astronomical unit was measured accurately?
17. Which would have a shorter orbital period, a planet orbiting a massive star at 3 A.U.
or a planet orbiting a low-mass star at 3 A.U.? Explain your answer.
18. If a planet orbiting a massive star has the same orbital period as a planet orbiting a
low-mass star, which of the planets orbits at a greater distance from its star? Explain
your answer.
19. What two things does the escape velocity depend on?
20. Why does the planet Saturn with over 95 times the Earth's mass have a smaller escape
velocity at its cloud tops than the Earth has at its cloud tops?
21. How can you predict the orbital period of Jupiter's satellite Europa from observations
of the other jovian moon Io?
22. The Hubble Space Telescope orbits the Earth 220 kilometers above the surface and
takes about 1.5 hours to complete one orbit. How can you find out how far up to put a
communication satellite, so that it takes 24 hours to circle the Earth? (Such an orbit is
called a ``geosychronous orbit'' because the satellite remains above a fixed point on
the Earth.)
23. Find out how long it will take the Cassini spacecraft to travel to Saturn 9.5 A.U. from
the Sun. (Hint: Lookup the Hohmann Transfer Orbit on the internet.)