Year 12s: what will be the first way you research your future options? >>

Gravitational Orbit Help

matt2minger

Hi,

I got this question:

I used v = sqrt(GM/r)

and then T = (2 x pi x r)/(V)

However i got a minus time? how come

Reply 1

matt2minger

i have just tried using v=rw in the forumla

r^2 w^2 = GM/R

w = sqrt(GM/r^2)

T = 2xpi / w

But i still get a wrong asnwer?

Reply 2

teachercol

I dont see how anything can be negative.
Did you convert Km to m?

Reply 3

matt2minger

no should i have though?

Reply 4

Morbo

You got a negative time? How on Earth did you do that?

Centripetal force:

Unparseable latex formula:

\displaystyle \\ F = -\frac{mv^2}{r} = -\frac{GMm}{r^2}[br]\\[br]\\ \Rightarrow v^2 = \frac{GM}{r}

Then use:

\displaystyle v = r\omega = r\frac{2\pi}{T} \Rightarrow T = \frac{2\pi r}{v} = 2\pi \sqrt{\frac{r^3}{GM}}

This also derives a specific case of Kepler's 3rd Law:

\displaystyle T^2 \propto r^3

Reply 5

matt2minger

Hi,

I got this answer now

Reply 6

teachercol

Lol - thats way too big

Reply 7

teachercol

matt2minger

no should i have though?

yes

Reply 8

Morbo

matt2minger

Hi,

I got this answer now

Your value for G is wrong, and you have neither used the correct value for r, nor converted to the correct units.

r^3/T^2=GM/4PI^2

should be 1.7 hours

Latest

Articles for you

Your guide to handling revision and exam stress

Open days: five mistakes to avoid

Help! I’m having second thoughts about my uni choice

Why I loved studying online

Gravitational Orbit Help

Related discussions

Latest

Trending

Trending

Articles for you