Me winning a queen for a rook was not a good move?

Sometime i am confused by the game analyzer. 

In this picture I just moved my rook from g1 to c8. The analyzer deemed this was excellent (not shown in my pictures). But in the next move I capture whites queen with Rxc5. The analyzer thinks I am stupid: It says I should have placed my rook (Ra1) behind the passed pawn on a4.

Seriously!? Any suggestions for how Ra1 would be better winning tactics? 

another proof that computers are scumbags

After White recaptures your Rook, they can just advance their a-Pawn and promote it, and there's nothing you can do about it. Not capturing the Queen keeps the position more complicated; your move just sped up the inevitable.

Your pretty lost in any case, but Rxc5 transposes into a pure king and pawn ending where your opponent has 4 pawns to your 1. So that's hopeless.

I think it wanted you to try to take out the other pawns first because it is clearly losing after this.