Hi, I have a couple of questions from a statics assignment that I'm in need of help on. Here's what I have so far:(adsbygoogle = window.adsbygoogle || []).push({});

http://216.170.11.226/pub/6131.jpg

Two rods are connected by a slider block as shown. Neglecting the effect of friction, determine the couple Ma required to hold the system in equilibrium.

And this is what I believe the forces are:

http://216.170.11.226/pub/6131-2.jpg

It would seem to me that the external forces are irrelevant to this problem, but I'm guessing not. What I came up with for this problem is:

Sum of moments about B=0 => -25+Nd*271.89=0 => Nd=0.0919

Sum of moments about A=0 => -.0919*150+Ma=0 => Ma=13.79 N*m

I know the answer is Ma=15.22 N*m. I'm guessing that I also need to consider external forces or something.

The next problem is

http://216.170.11.226/pub/6129.jpg

The double toggle mechanism shown is used in a punching machine. Knowing that the links AB and BC are each of length 150 mm, determine the couple M required to hold the system in equilibrium when Phi=20 (degrees).

Once again, my analysis of the problem is:

http://216.170.11.226/pub/6129-2.jpg

Obvious things are:

Dy+Ey+Ay+800=0

Dx+Ex+Ax=0

sum of moments about B of AB=0 => M+By*150*cos(30)+Bx*150*sin(30)=0

Since AB is a two-force body, Bx=B*cos(30), By=B*sin(30) and A=-B.

B'x=-Bx

B'y=-By

Cx=C*cos(30)

Cy=C*sin(30)

sum of moments about C of BC=0 => -B'x*150*sin(30)+By*150*cos(30)=0

sum of moments about B of BC=0 => -Cy*150*cos(30)+Cx*150*sin(30)=0

And so on and so forth. If I continue in this manner I figure I'll end up with something around 24 equations, there has got to be a simplier method. Any idea what that might be?

Any hints or help would greatly be appreciated.

Thanks

-Aaron

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# Homework Help: A couple of statics questions

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