Keplers Law question (1 Viewer)

[ausm8]

Hi, I have this question

"A Planet in another solar system has three moons, all of which travel in approximate circular orbits. Use the Table to answer the following Questions:

Moon Radius in Orbs Periods in Reps
Alpha 4 16
Beta 9 54
Gamma 2.5 ?

a) Use the data to show that Kepler's 3rd law obeys for Alpha and Beta
b) Calculate the period of revolution in reps, of Gamma
c) Find the speed of moon Gamma, robs per rep"

I have never heard of the units Orbs, Reps and Robs.
Can someone please explain either the conversion of the units or how to approach this question.

Thanks

 

[Ioup]

Ignore the unfamiliar units when doing the calculation.
use r3/Tsquared=r3/tsquared.
Since Keplers Law is a formula of ratios they should cancel each other out.
I got something like 7.9 reps for Gamma..
But knowing my calculations its probably off.... by alot...
Anyway thats the premise of answering the question though.
And with the last questions just use v=2pier/t. Robs per rep just means rob/rep just like kilometres per hour =km/hr.
I hope thats right....

 

[Riviet]

I have absolutely no idea what these units are. Never seen them in a textbook before either. But I think just substituting the numbers into the formula and ignoring the units should yield the right answers.

 

[ausm8]

Ignore the unfamiliar units when doing the calculation.
use r3/Tsquared=r3/tsquared.
Since Keplers Law is a formula of ratios they should cancel each other out.
I got something like 7.9 reps for Gamma..
But knowing my calculations its probably off.... by alot...
Anyway thats the premise of answering the question though.
And with the last questions just use v=2pier/t. Robs per rep just means rob/rep just like kilometres per hour =km/hr.
I hope thats right....

Thanks for your help,

For Gamma I get 10, from the method you used. The last question seems to be fine. Also, for part a how would you write it out, like a maths proof or...?

Thanks for your help again I appreciate it very much

 

[ausm8]

Just going through the problem again, I have worked how to show the answer in Part a)

Thanks for your help

 

[WouldbeDoctor]

Where did you get this question, the physic text book?? Cause I do not remember doing it.

 

[Riviet]

It's more likely to be from a worksheet.

 

[501n2u]

lols did you get that question off the matrix booklet?