| Author |
Comment/Response |
Peter Pein
|
 09/24/06 11:14pm
Hi,
1. Solve the differential equation:
In[1]:=
sol = y[t] /. First[DSolve[m*Derivative[2][y][t] + b*Derivative[1][y][t] + k*y[t] + m*g ==
0, y[t], t]]
Out[1]=
-((g*m)/k) + E^(((-b - Sqrt[b^2 - 4*k*m])*t)/(2*m))*C[1] +
E^(((-b + Sqrt[b^2 - 4*k*m])*t)/(2*m))*C[2]
2. select the term in the sqrt:
In[2]:=
Cases[sol, Exp[y_] :> Cases[y, (s_)^(1/2) :> s, Infinity][[1]], Infinity, 1][[1]]
Out[2]=
b^2 - 4*k*m
And now you can do whatever you want with this term.
hth,
Peter
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