1. The problem statement, all variables and given/known data An asteroid which strikes the earth starts from rest a very large distance r from the earth (say r = ∞). What will its speed be when it hits the earth? (Use M = 6.0×1024 kg, r= 6.4×106 m, G = 6.7×10-11 m3 kg-1 s-2) 2. Relevant equations U=-GmM/r F=GmM/r^2 3. The attempt at a solution At r=∞ the potential energy is 0. I replaced F with m*a to get this: m*a=GmM/r^2 Dividing out an m and plugging in the numbers gets me 9.81 as the acceleration (which makes sense as that is the accepted value of acceleration for Earth). I don't know how I am supposed to find the velocity after this. The answer is 1.1*10^4 m/s. (I know the answer because it is a back-test, just need guidance on how it is done). Thanks!