Speed of a mass falling into a star given the mass and radius of the star

TobiasZed
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Homework Statement
Beginning at rest at an extremely large separation, a ball is released and allowed to fall toward a star of mass 3.90E+30 kg and radius 5.70E+7 m. What is the speed of the ball when it reaches the surface?
Relevant Equations
square root of (2*G*M)/(r)
I tried the square root of ((2)(6.67*10^-11)(3.90E+30))/(5.70E+7)
I got 1.55*10^-5 and that is wrong. Maybe I am using the wrong equation but this is the one of professor gave me and I don't know what I am doing wrong :-(
 
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Check your calculation.
 
… and use units!
 
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