- #1
Foehammer
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Homework Statement
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)
Homework Equations
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U=-GmM/r
F=GmM/r^2
The Attempt at a Solution
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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!