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Complex Pulley System (five different pulleys) 
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#1
Jun909, 09:44 PM

P: 8

1. The problem statement, all variables and given/known data
We are asked to find the force (F) needed to maintain equilibrium. I've drawn a picture; the red, blue, and green ropes are three separate ropes. Block W has a weight of 500 lbs, pulley A has a weight of 10 lbs, and pulley B has a weight of 20 lbs. the picture: 2. Relevant equations Can't think of any, it seems like this problem just uses some common sense I am clearly lacking. 3. The attempt at a solution I think I figured out what the answer would be if you ignore the weights of the two pulleys. The tension would be 1/2 W on either side of pulley B, and therefore the tension pulling down on pulley A would be 1/2 W. Therefore, the tension on either side of pulley A would be 1/4 W, and since that rope is the rope to which the force F is applied, F=1/4 W=125 lbs. But I just don't know how to take into account the weights of the pulleys. Thanks for any and all help! 


#2
Jun1009, 01:10 AM

HW Helper
P: 4,437

There are three segments in the red rope. Total hanging weight is W+B. Find the tension in each segment. Apply the same thing to green rope.



#3
Jun1009, 05:17 AM

P: 8

So tension in the red rope would equal 1/3(W+B), and then tension in the green rope would equal 1/3(A+1/3(W+B)) ?



#4
Jun1009, 11:05 AM

HW Helper
P: 4,437

Complex Pulley System (five different pulleys)
Yes.



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