Force on door from two hinges - easy - help anyone?

[vtech]

torque/force problem - two door hinges - help anyone?

A large door of height - 2.1 m - along y-axis that extends vertically upward and width - 0.95 m - along x-axis that extends outward from the hinged edge of the door. A hinge at 0.30 m from the top and a hinge at 0.30 m from the bottom, each support half the door's mass which is 28 kg.

(a) In unit-vector notation, what is the force on the door at the top hinge?
___ N i +____ N j
(b) In unit-vector notation, what is the force on the door at the bottom hinge? ___ N i +____ N j


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I don't understand where the horizontal force - vector in i direction - is coming from if there's no horizontal movement and only gravity is acting along the y-axis or j hat

so my answers for the j hat vectors are simply 9.8x14= 137.2N which is the correct answer... but i don't understand parts A and C?

help anyone?

 

[vtech]

help please~!

anyone out there? i don't need to give me the answer... could anyone just point me in the right direction? how to find the i-hat vector forces in this problem?

thanksss a lot

 

[CartoonKid]

Take the moment about the bottom hinge to find the answer for a) and then swap to the top hinge to find b)

 

[HobieDude16]

i, too, am stuck on this problem, and what do you mean by take the moment? I am a bit rusty, and trying to remember that, but can't seem to remember... any help?

 

[CartoonKid]

First you draw the free body diagram. Putting in all the forces into the diagram, there are altogether 5 forces, 2 at each hinge and the door's self weight. There are 2 unknown forces in the diagram since you have been told that the vertical component at each hinge is half of the door weight. 2 unknown forces and 3 equations derived from the diagram, it can be solved.