Piece-wise second order differential equation Suppose I have some function f(x)

esbagoar7kh

esbagoar7kh

Answered question

2022-04-23

Piece-wise second order differential equation
Suppose I have some function f(x) which is equal to kx when x is negative and -kx when x is positive, and I have the following differential equation :
d2xdt2=k|x|=f(x)

Answer & Explanation

belamontern9i

belamontern9i

Beginner2022-04-24Added 19 answers

Step 1
For k=0, x(t)=c1t+c2.
For k0, start by multiplying both sides of your differential equation by x(t) and integrating in terms of t,
dxdtdtdt(dxdt)
=-k|x|dxdt12(dxdt)2
=-k|x|dx.
Therefore,
t+c1=±dx'-2k|x|dx
1) If x>0, |x|dx=xdx=x22+c2 Therefore,
t+c1=±dxc2-kx2
=±1ktan1(kxc2kx2)
x(t)=±c2ksin(k(t+c1))sgn(cos(k(t+c1))).
2) If x<0, |x|dx=-xdx=-x22+c2
t+c1=±dxc2+kx2
=±1ktanh-1(kxc2+kx2)

x(t)=±c2ksinh(k(t+c1)).

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