physics
posted by Al on .
Assume that the mass of a neutron star is 1.5 times that of the Sun and the radius of the neutron star is 10 km. Ignore effects of Special Relativity.
What is the approximate speed at which an object released from far away (at zero speed) reaches the surface of a neutron star?
A. 8*10^7 m/s
B. 9*10^7 m/s
C. 2*10^8 m/s
D. 3*10^8 m/s
Thank you.

C.
M=1.5•1.98•10³º kg
G =6.67•10⁻¹¹ N•m²/kg²
mv²/2=GmM/R
v=sqrt{2GM/R}=2•10⁸ m/s 
Hi, Elena. Thanks for helping me with the neutron star problem. I knew the formula, but kept getting answers that were not close to the possible choices. What variables did you use. Thanks again for your help.

v=sqrt{2•6.67•10⁻¹¹•1.5•1.98•10³º/10⁴}=
=1.99•10⁸ m/s ≈2•10⁸ m/s