Torque question

[AndyK]

Having an issue with this problem of torque/tension

Here is a gallery with a screengrab of the problem and the solution.

http://imgur.com/a/50HPX

Honestly, I'm just generally confused about how to solve this problem, and I feel the solution just confuses me further. I'd be grateful if anyone could shed some light and explain this problem more thoroughly.

Thanks in advance.

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[justadream]

@AndyK

Intuitive (Common Sense Approach):
If you just imagine this scenario in real life, you know that because the wall is pulling the horizontal bar downwards, the slanted bar is going to push INTO the wall. Thus, the wall must push OUTWARDS to counteract that. From this, you know the wall is pushing to the RIGHT (eliminate A, B)

Now think about what happens if you lengthen the horizontal bar. To me, it just seems intuitive that if you made the bar really really long, it would cause the slanted bar to push into the wall harder and harder. To counteract this, the wall must push outwards (to the right) with a greater and greater force. Thus, l must be in the numerator. That gets you choice C.


Other approach:
As with the answer explanation, let your pivot point be point A. Everything at the pivot point cancels out. Ok now only two forces remain for consideration:

1) The horizontal bar: it is going to move clockwise so it will have a negative torque that is equal to lT.
2) The wall: will exert some type of force (either inwards or outwards on the bar - as I established above, it will exert an outward force). Since the wall will exert an outward force, it will be moving counterclockwise. This is why the torque component here is positive and equal to dF.

Since we are at equilibrium, the two forces must sum up to 0.
Solve for F and you're done.

 

[ayocaptain628]

Having an issue with this problem of torque/tension

Here is a gallery with a screengrab of the problem and the solution.

http://imgur.com/a/50HPX

Honestly, I'm just generally confused about how to solve this problem, and I feel the solution just confuses me further. I'd be grateful if anyone could shed some light and explain this problem more thoroughly.

Thanks in advance.

Where did you get this question
I'm curious it looks like their answer explanations r good

 

[Czarcasm]

Where did you get this question
I'm curious it looks like their answer explanations r good

NOVA Physics, really good book.

 

[ayocaptain628]

NOVA Physics, really good book.

thx m8 xxx