Hi,
I'm following the "Introductory Differential Equations using Sage" book
by David Joyner and Marshall Hampton, and I got stuck at example 1.8.1.
I have coded it a bit differently, but the first part of the problem is
OK, as far as I can see it:
===============
var('t')
v = function('v',t)
m=100;g=98/10;k1=15;k2=100
de1 = diff(v,t) + k1/m * v - g
s1 = desolve(de,v,[0,0])
de2 = diff(v,t) + k2/m * v - g
st2 = desolve(de2,v,[0,s1(t=30)])
s2 = lambda tr: st2(t=tr-30)
int1 = integral(s1,t)
int2t = integral(st2,t)
int2 = lambda tr: int1(30) + int2t(tr-30) - int2t(0)
plot(int1,0,30)+plot(int2,30,50)
=====================
This will show me the distance travelled by somebody jumping from a
plane, the first 30 seconde free fall, and the following 20 seconds with
a parachute.
The graph comes out nicely. Now I want to find exactly at what time he
will touch the ground (assuming the jump was from 2Km). From the graph I
know that it is after second 30, so I was hoping to do just:
solve([int2(t)==2000],t)
but this gives the not very helpful:
[t == -1/441*(2940*e^(-t + 30) - 2499*e^(-t + 69/2) - 12531*e^(9/2) +
16660)*e^(-9/2)]
What am I doing wrong?
Thanks,
--
Ángel de Vicente
http://angel-de-vicente.blogspot.com/
--
To post to this group, send email to [email protected]
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/sage-support
URL: http://www.sagemath.org
