[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/b7tKz.png
Goal is to solve for the voltage u2(t)

Okay so I'm some what confused on this. I solved the transfer function \$Z(s)\$ earlier in the top circuit, which is simply just Z. The voltage across Z in the top circuit is $$u_1(t)=5e^{(-100*t)}u(t)$$ and the current source is j(t)=u(t), where u(t) is the step function. Z is a circuit system itself with no independent sources and all initial values are zero. 

Using basic principles for u2(t) you obtain e(t)*Z/(R+Z), where again e(t)=u(t), so it's u(t)*Z/(R+Z). Obviously just from that equation you cannot solve the voltage. I'm thinking this has something to do with the frequency response, but I don't know how I'm supposed to use it for this problem. 

Zs in both circuits are the same