Differential equations (swinging door)

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SUMMARY

The discussion centers on solving a differential equation related to a swinging door with a damper, characterized by the polynomial 0.5*r^2 + 1.5*r + 0.625. The general solution for the initial conditions x(0)=0.25 and v(0)=v_0 is derived, leading to the equation (0.25-(v_0+0.125)/(-2))*e^(-0.5*t)+((v_0+0.125)/(-2))*e^(-2.5*t). The participant concludes that the initial velocity must be less than zero for the door to swing through the closed position and return from the opposite side, indicating a successful resolution of the problem.

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Homework Statement


[/B]
There is a swing door with a damper. The characteristic polynomial (I have done it correctly) is:
0.5*r^2+1.5*r+0.625

General solution for x(0)=x_0 and v(0)=v_0 is (I have found it without a problem):

(1.25*x_0+v_0/2)*e^(-0.5*t)+((v_0+0.5*x_0)/(-2))*e^(-2.5*t)

Now the hell begins:
for x(0)=0.25
What can you say about the initial velocity of the door if, once the door is let go, it swings through the closed position and then swings back from the other side? (a numerical value and an appropriate inequality should be given)

The Attempt at a Solution


[/B]
Constants c_1 and c_2 given the initial conditions (x_0=0.25).

c_1+c_2=0.25
v_0=(0.25-c_2)*(-0.5)-c_2*(2.5)

The new solution:

(0.25-(v_0+0.125)/(-2))*e^(-0.5*t)+((v_0+0.125)/(-2))*e^(-2.5*t)

Well, now I am at my wits' end. I guess the velocity at the equilibrium position should be less than 0.

 
Last edited by a moderator:
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Hi, guys, I have solved it at last. No help necessary. Phew.
 
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