Statics Questions - Equilibrium in a pulley system

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Wilson123
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Homework Statement


Find the value of W to maintain equilibrium
Diagram of a pulley system: two pulleys mounted on supports 4 m apart, with a rope from each pulley to an 80 kg block hanging in the middle, and a weight W hanging from each pulley's rope end; a vertical height of 60 cm is marked on the right.


Homework Equations

The Attempt at a Solution


I have split the system into two, creating a triangle. From this I have a right angle triangle with an adjacent of 2m, opposite of 0.6m and an hypotenuse of 2.088m (calculated through pythag). I have then worked out the angle at the pulley as 16.7 degrees. However I do not know how to now find W, I think it may have something to do with the equation 40kg x g x cos(90-16.7) + 40kg x g x sin(90-16.7), but this isn't given me the kind of answer I expected so I'm not sure if it's right.
Figure 2: symmetric pulley system with an 80 kg block hung from a cord over two pulleys, with masses W on each side. Span 4 m, height difference 600 mm, annotated 2 m, 0.6 m and 2.088 m.


Any help on the next step would be much appreciated!
 
How about analyzing the forces acting at the point where the ropes connect to the 80 kg mass. Apply the conditions for equilibrium.
 
Doc Al said:
How about analyzing the forces acting at the point where the ropes connect to the 80 kg mass. Apply the conditions for equilibrium.
Am I right in thinking the forces are acting like this?
Free-body diagram of a pulley system: a central block hangs from a point held by two strings over pulleys on a horizontal bar, with tension T shown along each string and a downward weight arrow on each block, and angle theta marked between the strings at the central junction.
 
Wilson123 said:
Am I right in thinking the forces are acting like this?
Yes, that's exactly right. And if you set up the equilibrium equations, you can solve for T.