Calculating Torque of a Uniform Door Due to its Own Weight

[mikefitz]

Homework Statement

A uniform door
weighs 50.0 N and
is 1.0 m wide and
2.6 m high. What is
the magnitude of
the torque due to
the door's own
weight about a
horizontal axis
perpendicular to the
door and passing
through a corner?

http://img519.imageshack.us/img519/5172/untitledwp6.png


question; where does t=rF come from? it is not found on my equation sheet...

 

[radou]

question; where does t=rF come from? it is not found on my equation sheet...

This is extremely elementary. What is the definition of the torque?