Basic maths frameworks

How to find the reaction force on B in below frameworks?

http://oi56.tinypic.com/a13f6e.jpg

step by step explanation would be appreciated because I can't understand my freak tutorial !

thanks

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- Apr 21st 2011, 07:49 AMsilvercatsFrame works help
Basic maths frameworks

How to find the reaction force on B in below frameworks?

http://oi56.tinypic.com/a13f6e.jpg

step by step explanation would be appreciated because I can't understand my freak tutorial !

thanks - Apr 21st 2011, 08:04 AMabhishekkgp
- Apr 21st 2011, 08:33 AMtopsquark
Also at B you have listed two different coordinate systems. You have to choose one of them and then stick with it, else you will get confusing answers.

-Dan - Apr 21st 2011, 08:52 AMsilvercats
- Apr 21st 2011, 08:53 AMsilvercats
- Apr 21st 2011, 09:00 AMsilvercats
To be clear,here is the answer they have given but i don't understand

AB ~ Y(2a cos 60)-x(2a Sin 60)-w(a cos 60) = 0

~ Y-(√3)x = w/2 ------- (1)

CD ~ y(2a cos 60)+x(2a Sin 60) + w(a cos 60)=0

~ Y+(√3)x=-w/x -----------(2)

and they solve it and I am like :O - Apr 21st 2011, 12:30 PMtopsquark
- Apr 21st 2011, 06:03 PMsilvercats
- Apr 21st 2011, 08:23 PMabhishekkgp
the forces applied to AB at the point A by the rod AC has not been considered. why?

consider this force too in the FBD. It will have two components. same story will be there with point C on rod BC. again two more unknown forces are introduced.

we have a total of 6 unknowns now. x,y, two components of force on point A, and two components of force on point B.

you must be aware of the fact that we can have three equations of statics for a rigid body in two dimensions.Consider rod AB, these three equations can be:

1) summation of torques about point A is zero.

2)summation of torques about point B is zero.

3)vector sum of the forces acting on AB is zero.

similarly we will have 3 more equations when we consider rod BC's statics.

hence 6 equations and six unknowns.

Did this help? - Apr 21st 2011, 08:37 PMabhishekkgp