In article ,
Harry K wrote:
(John Cochran) wrote in message ...
In article ,
Harry K wrote:
SNIP....
Here is your diagram of the original problem.

Now for the situition that we have here


|
|
O\
| \
| \
| \ --- 10 feet of rope with 5 feet on both sides of
| \ pulley. The weight is 5 feet below the pulley.
| \
| \
| \
| . Anchor
+----+---+
| 40 lbs |
+--------+


Now we both agree that the force on both legs of the rope is 40lbs
Where does the second 40 come from?

To make it clear that it is the -same- 40 lbs:

Tie the right leg to the weight. That is the same as tieing it to an
anchor.

No it isn't. If you tie the other end of the rope to the load instead
of the anchor, this is what you get.


|
|
O
| |
| |
| |
This half ----- | | --- This half of the rope has 20 lbs of tension.
of the rope | |
has 20lbs of | |
tension | |
| |
+---+-+--+
| 40 lbs |
+--------+


For the situition that you have


|
|
O\
| \
| \
This half ------ | \ --- This half of the rope has 40 lbs of tension
of the rope has | \
40 lbs of | \
tension | \
| \
| . Anchor
+----+---+
| 40 lbs |
+--------+

No matter how you do it, in order to support the 40lb load, the sum of
all ropes attached to the load has to add up to 40lbs. If you're using
a simple pulley at the top and attach both ends of the rope to the load,
then the rope has a tension of 20lbs and both sides add up to a total
of 40 lbs. If you instead attach one end of the rope to an anchor, then
the rope has an tension of 40 lbs and the hook at the top is having to
support a total of 80 lbs.

The weight will remain quite nicely right where it is.
What is the pull on the hook?? Where did the 40 lbs go??

I hope you answer this as you do appear to know what you are talking
about. Just don't let what seems logical lead you down stray paths.
Yes, on first glance the original problem appears to need a 80 lb
strain but unfortunately it isn't true in real life. A simple test (or
reference to any physics text) will show you in less than a minute.

Harry K