I found the answer,
Vec2 nokta = b2_balon.getWorldPoint(new Vec2(0, 1));
b2_balon.applyForce(new Vec2(1 ,0), nokta);
However, I still wonder why the other method doesn't work. Maybe, iforce2d knows because I found the solution at http://www.iforce2d.net/b2dtut/forces link. Thanks iforce2d :).