Is my forces diagram correct?

  • #1
Femme_physics
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(static equilibrium problem)

Homework Statement




Calculate the force R that acts on the axis of the crane (O), if the crane lifts in a constant speed a mass of 500 kg. The incline angle of the cable to the horizontal line is 45 degrees. Do not consider pulley friction.

The answers are:

R = 9063.23 [N]
Beta = 67.5 degrees

[PLAIN]http://img130.imageshack.us/img130/2276/forcesquest.jpg [Broken]



The Attempt at a Solution



I've only made a force diagram to ask you guys whether it's correct.

[PLAIN]http://img339.imageshack.us/img339/7528/forces.jpg [Broken]


*sighs* Truth is playing with triangles, law of Sines, and sum of all forces on X and Y is getting me nowhere -- but is this the way to solve it? I think that if my force diagram is correct it should be easy...just too many unknowns....
 
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Answers and Replies

  • #2
PhanthomJay
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You are doing more work than necessary...the OP just wants the force applied at O, so draw a FBD of the pulley, note the tension in the rope, and use Newton 1 in the x and y directions to solve for Rx and Ry...and Pythagorus to solve for R. The direction of R must be along the bisector of the angle between the ropes.
 
  • #3
Femme_physics
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Well, I've taken your advice and I'm inching close to the answer in terms of the numerical result but still a bit off... it seems to make since though... (angle is a piece of cake once I have the correct Rx and Ry....clear I don't yet)

I attached the file of my new diagram and method to solve it...do you mind taking a look?
 

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  • #4
PhanthomJay
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Well, I've taken your advice and I'm inching close to the answer in terms of the numerical result but still a bit off... it seems to make since though... (angle is a piece of cake once I have the correct Rx and Ry....clear I don't yet)

I attached the file of my new diagram and method to solve it...do you mind taking a look?
Again your equations are good but your math is lousy :wink:. Add up mg and Tsin45 again...
 
  • #5
Femme_physics
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Ah....it's that stupid calculator *embarrassed grin*.....thanks a lot phantom :D What'd I do without you!
 
  • #6
PhanthomJay
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Ah....it's that stupid calculator *embarrassed grin*.....thanks a lot phantom :D What'd I do without you!
Well,without me, you can always count on nvn or tiny-tim...and a host of others...:wink:
 
  • #7
Femme_physics
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Hehe... I love this forum. Best stuff on the internet!
 

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