# Central forces in elliptic and parabolic orbits

1. Nov 25, 2011

### armin.hodaie

hi,can anyone solve this two problems??
these are from the "textbook on spherical astronomy" written by W.smart
chapter five,problem number 18 and 19,Euler's theorem and Lambert's theorem
thank you ;-)

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2. Nov 25, 2011

### BruceW

Is this homework? You should try to do the problem yourself first. We are only meant to help on homework. P.S. the .bmp image is a bit difficult to read.

3. Nov 26, 2011

### armin.hodaie

yes,this is homework.i have been trying to solve this two question for more than a week,but i cant solve it ;-(

4. Dec 2, 2011

### armin.hodaie

nobody????really????

5. Dec 2, 2011

### BruceW

You haven't tried the questions yourself yet, so it is hard to give help. Also, I can't read the bmp image. And I'm guessing that's why there haven't been other replies yet.

6. Dec 4, 2011

### armin.hodaie

dear BruceW,
i have been trying for more than a week,but i cant solve them,so dont tell me that i havent tried !!!!
these are not simple problems :D
bmp files are readible,but i will write down questions right now !!!!

1.if r and r1 are the radii vectors of two points C and C1 in a parabolic orbit and if k is the distance C-C1.prove that the time in the orbit between C and C1 is:

(T0/12pi)[((r+r1+k)/a)^(3/2)-((r+r1-k)/a)^(3/2)]
where T0 is the length of the sidereal year and 'a' is the semi-major axis of the earth's orbit

2.if r and r1 are the radii vectors of two points C and C1 in a elliptic orbit and if k is the distance C-C1.'t' the time required by the planet to move from C to C1 and T the orbital period,prove that:

(2pi*t/T)=H-sin(H)-(H1-sin(H1))

where sin(H/2)=(1/2)((r+r1+k)/a)^(1/2)
sin(H1/2)=(1/2)((r+r1-k)/a)^(1/2)

7. Dec 4, 2011

### BruceW

the bmp is not completely readable, but thanks for writing it out, I know what it means now.

Maybe you have tried, but you haven't written anything on this thread. You've just asked for someone to solve them for you. The idea of this forum is that you post your working and/or say where you are stuck, then people try to help.

I know it is a pain to write all your working here, but otherwise, I don't know how to help.

8. Dec 4, 2011

### BruceW

The general idea is to use your knowledge of parabola and ellipses to show why the theorems must be true.

The first question is weird because it talks about a parabolic orbit and mentions the Earth's orbit, which is definitely not parabolic.

9. Dec 7, 2011

### armin.hodaie

i wont write my workings here,and i think there is no one to help me.this forum is really weak,bye4ever

10. Dec 7, 2011

byebye