- #1

Latinized

- 4

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## Homework Statement

I'm not asking for a full on solution to my question, but instead wanted to know what was the difference in these two questions. So, here are the two questions

1) A space station of radius 90 m is rotating to simulate a gravitational field.

What is the period of the space station’s rotation so that a 70 kg astronaut will experience a normal force by the outer wall equal to 60% of his weight on the surface of the earth?

Now the solution to the equation is fairly simple for me,

**however I don't get why the force of gravity does not matter for the centripetal force in this question.**

Fnet = mac

Fn = m4(pi)^2 (r)/ T^2

0.60 mg = m4(pi)^2 (r)/ T^2

T = 25s

While in this question:

2) A 720 kg communication satellite is in synchronous orbit around the planet Mars. This synchronous orbit matches the period of rotation so that the satellite appears to be stationary over a position on the equator of Mars. What is the orbital radius of this satellite?

Here, in this question,

**the force of gravity does matter for the centripetal force. Why is that when #1 it didn't matter.**

Solution btw:

Fg = mac

GmM/R^2 = m4π^2/ T^2

r = 2.0 x 10^7 m

Thank you very much! Sorry for the long post.