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## Homework Statement

#1

A satellite is in a circular orbit around an unknown planet/ The satellite has a speed of 1.70 x 10

^{4}m/s, and the radius of the orbit is 5.25 x 10

^{6}m. A second satellite also has a circular orbit around this same planet. The orbit of this second satellite has a radius of 8.60 x 10^6 m. What is the orbital speed of the second satellite.

#2

The moon orbits the Earth at a distance of 3.85 x 10

^{8}m. Assume that this distance is between the centers of the Earth and the moon and that the mass of the Earth is 5.98 x 10

^{24}kg. Find the period for the moon's motion around the Earth. Express the answer in days and compare it to the length of a month.

## Homework Equations

I have no clue. Maybe this?

v = sqrt(GM/r)

F = G (m

_{1}m

_{2}/r

^{2})

a = v

^{2}/ r

a = 4pi

^{2}r / T

^{2}

## The Attempt at a Solution

# 1: Well, I know there is something that the two satellites could be compared to, but I can't figure what. I tried a futile stab at the question by using v

_{1}

^{2}/ r = v

_{2}

^{2}/ r but that didn't give me the right answer.

The answer at the back of the book is 1.3 x 10

^{4}m/s.

# 2: I don't even know how to get started on this question...I know I have radius and mass of the Earth, and I need to find the period.

Any help towards these questions would be

__greatly__appreciated!