# Polar coordinate problems

1. Sep 23, 2008

### imsoconfused

HELP!!!! I just got this assignment over the email a couple hours ago and it's due in the morning and I have no clue how to do these problems! I've spent a few hours trying to figure this stuff out on my own, but I'm down to these last few and I just can't do it. if you can answer one or more, I really appreciate anything AT ALL. I'm sorry I don't have much done already, but I've got a brain block and I'm starting to panic. please help!!!

2. If a satellite circles the earth at 9000 km from the center, estimate its period T in seconds.

3. Convert 1/r = C - Dcos(theta) or 1= Cr-Dx into the xy equation of an ellipse.

5. The Earth takes 365.25 days to go around the sun at at distance d = 93 million miles = 150 million km. find the mass of the sun.
F=ma=constant/r^2.

Last edited: Sep 23, 2008
2. Sep 23, 2008

### tiny-tim

Hi imsoconfused!

2. Either compare t with the period of the moon (erm … that's one month! ) …*that only works if you know how far away the moon is, of course.

Or work out the gravitational force on it, by comparing it with g at the earth's surface … that only works if you know the radius of the earth … and then use centripetal acceleration

3. Sep 23, 2008

### HallsofIvy

Staff Emeritus
Multiply through by r first. r= [itex]\sqrt{x^2+ y^2} and r cos(theta)= x. You may need to square both sides of an equation to get rid of the square root and get the (standard)equation of an ellipse.

Problems 2 and 5 are not mathematics problems. They are physics problems and I would be surprised if your book does not have formulas that apply directly.