What is the Mass of the Planet in Scientific Notation?

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The discussion revolves around calculating the mass of a planet in relation to a star, using given orbital radii and the star's mass. The participant is confused about how to apply the provided data, specifically the distances in kilometers and the mass of the star. A suggestion was made to treat the problem as a center of mass issue, indicating that the planet's mass should be significantly smaller than the star's due to its greater distance from the center of mass. The participant attempted a calculation but expressed uncertainty about its accuracy and the units used. Overall, the thread highlights the challenges of applying physics concepts to solve a university assignment problem.
free_spirit
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Hi all :)

Hope the day has been good to you...i am stuck on a question for my uni assignment, and have been stuck on this one for about 3 days to no avail...i don't even know where to start. I'm not too sure whether i need a certain equation for the question or if i have to come up with one using the information in the question...
If anyone could please help me through it would be greatly appreciated as I've only got 4 days left...if not thanks for looking anyways :)


There once was a planet - quite far
In orbit around a star
The star’s mass was ms
The planet’s mass you assess
Using the orbital radii, r


You can assume the radius of the planet’s and the star’s circular orbits around the
centre of mass of the system are rp = 1.5 × 108 km and rs = 1.0 × 106 km, respectively, with
ms = 2.0 × 1030 kg.

Calculate the mass of the planet, mp, showing all your workings and giving your answer in scientific notation to the appropriate number of significant figures.


Any help would be amazing as I'm at my wits end !
Many Thanks,

Ax
 
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So far all the info i have is that;

a) the star is 1 million miles from the centre of mass
b) the planet is 150 million miles from the centre of mass; and
c) both bodies are in circular orbits to the centre...

so I'm not too sure how to use this data to calculate the answer...

Ax
 
free_spirit said:
So far all the info i have is that;

a) the star is 1 million miles from the centre of mass
b) the planet is 150 million miles from the centre of mass; and
c) both bodies are in circular orbits to the centre...

so I'm not too sure how to use this data to calculate the answer...

Ax

I think I would treat it as a simple centre of Mass problem. With the planet 150 times forther from the centre of mass I think it should simple be 1/150 th of the mass of the Sun.
 
ok thanks very much PeterO :)

i have done a calculation but am not too sure whether this is correct at all...

mp = rp x rs
ms

so,

mp = 1.5 x 108km x 1.0 x 106km
2.0 x 1030kg

mp = 150 000 000 000 000
2.0 x 1030kg

mp = 0.000 000 000 000 000 075 ??

ok, so i am also now thinking that this is incorrect...gah !

thanks for the help though, much appreciated :)
 
free_spirit said:
So far all the info i have is that;

a) the star is 1 million miles from the centre of mass
b) the planet is 150 million miles from the centre of mass; and
c) both bodies are in circular orbits to the centre...

so I'm not too sure how to use this data to calculate the answer...

Ax

How did you end up with miles as units when the problem appears to use kilometers?
 
oops !

my bad, sorry bout that i did mean kilometres...sorry been at this for a while now and my brain is kinda mushy...thanks for pointing that out
 

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