text: statics problem... please help me get started? the door brace ab is to be designed to prevent opening the door.  if the brace forms a pin connection under the doorknob and the coefficient of static friction with the floor is equal to 0.5, determine the largest length l the brace can have to prevent the door from being opened.  neglect the weight of the brace.  please help and explain how i would go about doing this... i don't get it always start with a diagram and a neat list of all the variables and constants that you know. write what you are trying to find, in this case l. then look for formulas with the knowns in them, find a formula or formulas to get what you want to know,  in this case friction = normal force x .5 (coeficient of friction) torque = force x length.  i can't tell from your description what the diagram would look like, but those two formulas should solve the proble.  if you can not figure this out, i recommend industrial design instead of engineering. i wish someone suggested that to me when i was in your position, because industrial designers actually do what i thought engineers did. engineers do what i thought managers did. and managers....well who knows what they do.