import math
def meteor(n):
	pi = math.pi
	ro = 1.2
	t = 0
	v = 0
	r = .01
	x = 1
	g = 9.8
	m = 21. * .001
        t_max = -(2 * x/g) ** (1/2) * 10.
        dt = t_max/n
        for i in range(n + 1):
                dx = v * dt
                x = x + dx
                if x < 0.:
			print(t)
                        return v
                F = pi/4 * ro * v ** 2 * r ** 2 - m * g
                a = F/m
                dv = a * dt
                v = v + dv
		t = t + dt
        return -999.
 
print(meteor(100000))

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