More advanced FBD problems-need some tips

[caddyguy109]

Some comments :

1. The reaction at B acts normal to the length of the rod.
2. The reaction at A acts vertically downwards.

Calling the angle between the rod and the vertical, X (so that tanX = a/2r) gives :

A + W = BsinX - - - (vertical forces)

P = BcosX - - - (horizontal forces)

Bd = (Wl/2)sinX + (Pl)cosX - - - (moments about A, with d^2 = a^2 + 4r^2)

Okay. So, what do I then use for the X value?

What does the Bd stand for?

 

[Gokul43201]

1. You only need values of sinX and cosX, which are respectively a/\sqrt{a^2 + 4r^2} and 2r/\sqrt{a^2 + 4r^2}.

2. A and B are the normal reaction forces by the pipe on the rod at those corresponding points (sorry about the terrible choice of notation). Perhaps I should have called them N_A, ~N_B.

3. d is the length of the rod inside the pipe. d = \sqrt{a^2 + 4r^2}.

 

[caddyguy109]

1. You only need values of sinX and cosX, which are respectively a/\sqrt{a^2 + 4r^2} and 2r/\sqrt{a^2 + 4r^2}.

2. A and B are the normal reaction forces by the pipe on the rod at those corresponding points (sorry about the terrible choice of notation). Perhaps I should have called them N_A, ~N_B.

3. d is the length of the rod inside the pipe. d = \sqrt{a^2 + 4r^2}.

FINALLY, something that makes sense!

Now, to arrange it all...

Now, I'm completely lost on the second one and a little on the third:
2) http://www.ihostphotos.com/show.php?id=182816"

This was said here:
"at least it's a 90 degree angle! and frictionless ...
try taking Moments around the place where the two F_N intersect
did you sum F_x and F_z first?"

but I just can't, for whatever reason, still figure out what the heck to do. ?

3) http://www.ihostphotos.com/show.php?id=182817"

Again, I was told this:
"this one's pretty easy. Moments around A, gives you T.
back-substitute into Sum F_x and F_z, to get reactions at pin."

and did this so far, until I tried to figure out what the tension TBE was and realized something was wrong:
http://www.ihostphotos.com/show.php?id=192075"

Anything in this one REALLY stick out to you?

 

[caddyguy109]

Anybody?

 

[caddyguy109]

Any help on the second two problems, based on what I said two posts up??

 

[caddyguy109]

Anybody?

 

[caddyguy109]

Okay, my last plead... ...

Can anyone help me figure out #2:
2) http://www.ihostphotos.com/show.php?id=182816

This was said here:
"at least it's a 90 degree angle! and frictionless ...
try taking Moments around the place where the two F_N intersect
did you sum F_x and F_z first?"

but I just can't, for whatever reason, get it going. Where the heck do I take the sum of moments about? And how do I then express the angle (theta) corresponding to equilibrium as a function of M, W, and L?

This is the LAST question for a while, I swear