The door weighs 200 lb. The center of mass of the door is point G. Determine the reactions at hinges A and B. NB : (a) Short hinges like these not designed to provide reaction moments in any direction. A long hinge, like a piano hinge on the top of a piano, is intended to provide a reaction moment. It's not always easy to tell in a homework or exam problem what the intention of the problem setter is. Some people will say "assume the hinges are well-aligned" which is code for saying "assume the reaction moments at the hinges are zero." These are short hinges; neglect any reaction moment. ) (b) This door is "improperly constrained". You'll be able to find all but two of the requested reactions. For the two undetermined reactions, you'll be able to find their sum, but not their individual values. (e.g. if we know r + y = 9, then r 9; y = 0 works, but so does r = -87; y = 96.) Hence, this is an example of "statically indeterminate" supports. (c) NB : is short for the Latin Nota bene which means "note well". 18 in. 24 in. 24 in. 18 in. 30 -y