2nd order System steady state error

[silentwf]

Homework Statement

The system's closed loop transfer function is given below, find K and $$\alpha$$ such that the input $$R(s) = 1/s^2$$ has no steady state error. (Hint: the system is not a unit feedback system)
[PLAIN]http://img829.imageshack.us/img829/9899/problempr.png

Homework Equations

not sure how many there are.

The Attempt at a Solution

So I made the system into a unit feedback system despite its hint...and it turned out..strange.
Another thing i don't understand is, with the conditions that the questions, i only get one equation to solve for k and $$\alpha$$, are there any others that i might be overlooking?


[PLAIN]http://img692.imageshack.us/img692/3111/solj.png

 

[CEL]

Homework Statement

The system's closed loop transfer function is given below, find K and $$\alpha$$ such that the input $$R(s) = 1/s^2$$ has no steady state error. (Hint: the system is not a unit feedback system)
[PLAIN]http://img829.imageshack.us/img829/9899/problempr.png

Homework Equations

not sure how many there are.

The Attempt at a Solution

So I made the system into a unit feedback system despite its hint...and it turned out..strange.
Another thing i don't understand is, with the conditions that the questions, i only get one equation to solve for k and $$\alpha$$, are there any others that i might be overlooking?


[PLAIN]http://img692.imageshack.us/img692/3111/solj.png[/QUOTE]

You used the wrong expression for the steady state error. You should have used the closed loop function and not the open loop G.