Thursday

August 21, 2014

August 21, 2014

Posted by **POD** on Monday, April 7, 2008 at 4:28pm.

please help!!!

- physics(please help) -
**drwls**, Monday, April 7, 2008 at 5:02pmThis calls for a combination of Kepler's third law (or Newton's gravitational and motion laws) and trigonometry.

Equating the gravitational attraction to the centripetal force tells you that

GM/R^2 = V^2/R = (2 pi R/T)^2/R

= 4 pi^2 R/T^2

Therefore

(4 pi^2/G M) = T^2/R^3

where R is the distance from the planet to the star. I will let r be the diameter of the star.

The angle subtended by the star in radians is theta = 2 r/R

Now, the star's density = M/[(4/3) pi r^3]

= M/[(4/3) pi R^3]*(r/R)^3

= 4 pi^2/(G T^2)(r/R)^3 / [(4/3) pi]

= 3 pi/(G T^2)/(theta/2)^3

= 24 pi/[G T^2 (theta)^3]

**Related Questions**

physics - a 9.9*10^23 kg planet orbits a star in a circular orbit. The planet ...

Physics help please - You are the science officer on a visit to a distant solar ...

Physics - planet orbits a star once every 2.84 10^7 s in a nearly circular orbit...

physics - Planet A and planet B are in circular orbits around a distant star. ...

physic - Planet A and planet B are in circular orbits around a distant star. ...

physic - Planet A and planet B are in circular orbits around a distant star. ...

Physics help please - You are the science officer on a visit to a distant solar ...

physics - Planets A and B orbit the same star. Planet B is four times further ...

physics - A planet orbits a star, in a year of length 4.46 x 107 s, in a nearly ...

Physics - I can not figure this out. You are the science officer on a visit to a...