Get records from multiple tables ordered by shared column

i'm new to rails and i don't know how to do this simple operation :

i have ,

class Section < ActiveRecord::Base
   has_many :articles
   has_many :questions
end

class Article < ActiveRecord::Base
   belongs_to :section
end

class Question < ActiveRecord::Base
   belongs_to :section
end

and i want to get all articles and questions under a certain section but sorted together by shared column 'updated_at' .

i tried including and joining them but failed to order them together .