 #1
Tom4
 4
 1
 Homework Statement:

A small asteroid of mass m = 1.50 × 10^13 kg collides with the planet Mars. The speed of the asteroid when it was very far from the planet was 3.60 × 10^3 m/s. Given that Mars has a mass M = 6.42 × 10^23 kg and a radius R = 3.39 × 10^6 m, and that the gravitational constant G = 6.67 × 10^−11 Nm^2/kg^2 the speed at which the asteroid impacts the Martian surface is:
A) 8.63 × 103 m/s.
B) 4.29 × 103 m/s.
C) 6.18 × 103 m/s.
D) 7.15 × 103 m/s.
 Relevant Equations:

u=GMm/r
k = mv^2/2
Since the radius is "very far", I cannot find the total mechanical energy by using the gravitational potential energy formula and find the kinetic energy at impact. I can't think of any other way to find final velocity without knowing the radius.