import math
def meteor(n):
r=.09
m=7
b=1.5e-3
x=200.*1000.
v=-20.*1000.
H=7.6*1000.
g=9.8
t_max=-x/v*10.
dt=t_max/n
for i in range (n):
dx=v*dt
x=x+dt
if x<0.:
return v
F=b*v**2*mat.exp(-x/H)-m*g
a=F/m
dv=a*dt
v=v+dv
return-999
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