Homework Help: Physics

Posted by Alex on Friday, January 11, 2013 at 12:48pm.

Black Holes are suspected when a visible star is being noticeably pulled by an invisible partner that is more than 3 times as massive as the Sun. A red giant star is accelerated in a linear direction by gravity at 0.075 m/s2 towards an object that is 9.4 x1010 m away.

a) What is the mass of the invisible star? Answer using scientific notation (eg. 1e+10)
b) By what factor is the star more massive than our Sun? Answer in decimal.

Physics - Steve, Friday, January 11, 2013 at 2:49pm
F = GMm/r^2
a = F/m = GM/r^2 = 6.673*10^-11 * M / (9.4*10^10)^2 = 0.075
M = 9.931*10^30

M/sun = 9.931*10^30 / 1.989*10^30 = 4.993

so, the red giant is 5 times as massive as Sol.

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