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I'm really just concerned with my math here because I know that I should think of a celestial object having mechanical energy and not total energy, but just using a planet and a star as an example, is this how I would find the Total Energy of a planet orbiting a star, knowing the mass of the planet, the mass of the star and the gravitational force in Newtons exerted on the planet?
Here' goes:
First [tex]E_{total}=E_k+E_p[/tex]
[tex]E_k=\frac{1}{2}mv^2[/tex]
[tex]E_{potential.grav.}=-\frac{Gm_1m_2}{r}[/tex]
We don't know the radius yet so...
[tex]r=\sqrt{\frac{Gm_1m_2}{F}}[/tex]
Nor do we know the velocity of the planet so...
[tex]v_p=\frac{2\pi r^2}{2\pi\sqrt{\frac{r^3}{GM}}}[/tex]
(M=mass of star)
So know that we have found both the velocity and radius...
[tex]E_{Total}=\frac{1}{2}m(\frac{2\pi \sqrt{\frac{Gm_1m_2}{F}}^2}{2\pi\sqrt{\frac{(\sqrt{\frac{Gm_1m_2}{F}})^3}{GM}}})^2-\frac{Gm_1m_2}{\sqrt{\frac{Gm_1m_2}{F}}}[/tex]
That equation becomes much simpler once you solve for r first.
[tex]E_{Total}=\frac{1}{2}m(\frac{2\pi r^2}{2\pi\sqrt\frac{r^3}{GM}}})^2-\frac{Gm_1m_2}{r}}[/tex]
Then back too:
[tex]E_{Total}=\frac{1}{2}mv^2-\frac{Gm_1m_2}{r}}[/tex]
I hope I haven't made it too complicated. I think my mistake is with finding the velocity of the planet by dividing distance by time, but I probably have more...
Thanks in advance.
Here' goes:
First [tex]E_{total}=E_k+E_p[/tex]
[tex]E_k=\frac{1}{2}mv^2[/tex]
[tex]E_{potential.grav.}=-\frac{Gm_1m_2}{r}[/tex]
We don't know the radius yet so...
[tex]r=\sqrt{\frac{Gm_1m_2}{F}}[/tex]
Nor do we know the velocity of the planet so...
[tex]v_p=\frac{2\pi r^2}{2\pi\sqrt{\frac{r^3}{GM}}}[/tex]
(M=mass of star)
So know that we have found both the velocity and radius...
[tex]E_{Total}=\frac{1}{2}m(\frac{2\pi \sqrt{\frac{Gm_1m_2}{F}}^2}{2\pi\sqrt{\frac{(\sqrt{\frac{Gm_1m_2}{F}})^3}{GM}}})^2-\frac{Gm_1m_2}{\sqrt{\frac{Gm_1m_2}{F}}}[/tex]
That equation becomes much simpler once you solve for r first.
[tex]E_{Total}=\frac{1}{2}m(\frac{2\pi r^2}{2\pi\sqrt\frac{r^3}{GM}}})^2-\frac{Gm_1m_2}{r}}[/tex]
Then back too:
[tex]E_{Total}=\frac{1}{2}mv^2-\frac{Gm_1m_2}{r}}[/tex]
I hope I haven't made it too complicated. I think my mistake is with finding the velocity of the planet by dividing distance by time, but I probably have more...
Thanks in advance.