It is known Neptune is 30 AU from Sun, it takes 164 years to complete one orbit around the Sun. Use this info. alone to estimate the mass of the Sun.

Should I use Newton's version of Kepler's 3rd law?

Question

It is known Neptune is 30 AU from Sun, it takes 164 years to complete one orbit around the Sun. Use this info. alone to estimate the mass of the Sun.

Should I use Newton's version of Kepler's 3rd law?

vincent-lyon.fr · Answer

Yes.

anonymous · Answer

But it says "using the info alone" so thats just orbital period, semi-major axis and unknown mass

anonymous · Answer

if i use newton's version then the G is an extra info

vincent-lyon.fr · Answer

You can't help it.
G is a universal constant, so you are probably allowed to use it.

anonymous · Answer

Ok so can u tell me whats the problem of this equation?

$$(164*365*24*3600)^{2}=\frac{(4\pi ^{2})[(30)(1.49*10^{8}])}{(6.67*10^{-11})(M)}$$

vincent-lyon.fr · Answer

I think you have forgotten to cube the radius of the orbit.

anonymous · Answer

oh right, i forgot to type in that but other than that?

anonymous · Answer

cus i can't get 1.99*10^30

vincent-lyon.fr · Answer

1au = 150 million km = 1.5 x 10¹¹ m

anonymous · Answer

dont i need to convert m to km? and even tho i used 10^11, i still can't get the ans.......