Balancing a teeter-totter problem

[johnrot]

this is teeter,it can rotate at point B
in first picture fan is turn off and teeter is in balance,point A is universal joint..
https://www.physicsforums.com/attachments/261054
now fan is turn ON and men is lean back to hold fan thrust...
Question is, will be teeter start rotate in clockwise or in counter clockwise direction?
https://www.physicsforums.com/attachments/261061two solution:

1) universal joint can't transfer moment only horizontal and vertical forces,so that mean that "side force" act in level of men feet,projection of this force is below point B so teeter will rotate in counter clockwise direction..
here is problem that "side force" is internal force in system but internal force can't "rotate system"..

2)only external force can "rotate system" so thrust at fan act above point B so teeter will rotate in clockwise direction
here is problem that u.j. can't transfer moment ,so how would thrust rotate teeter...

I am with solution 1)

What is your answer?

 

[A.T.]

...men is lean back to hold fan thrust...

Does his center of mass move horizontally while he leans back?

I am with solution 1)

Did you consider the horizontal force of the feet on the teeter?

 

[berkeman]

OP deleted his post after receiving the reply by @A.T. so we have restored the Original Post and the thread will remain locked for now.

@johnrot -- please do not delete or edit your OP after you have received replies. Check your PMs and let me know if you want this thread re-opened.

 

[berkeman]

New version of this thread is here: https://www.physicsforums.com/threads/teeter-tricky-problem.987781/#post-6329889