I don't understand this ship mechanics question at all

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TSR360
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#1
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#1
Q:
https://i.imgur.com/rxrZ2Pj.png
https://i.imgur.com/CvKu5hG.png

My forces diagram:
https://i.imgur.com/JMmlEcU.png

The tension of the cable should be 1200 N. What did I do wrong?
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RDKGames
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#2
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#2
(Original post by TSR360)
Q:
https://i.imgur.com/rxrZ2Pj.png
https://i.imgur.com/CvKu5hG.png

My forces diagram:
https://i.imgur.com/JMmlEcU.png

The tension of the cable should be 1200 N. What did I do wrong?
There are 4 sailors each providing a force of 300N ... so total tension is 4 x 300N.
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TSR360
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#3
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#3
(Original post by RDKGames)
There are 4 sailors each providing a force of 300N ... so total tension is 4 x 300N.
In the textbook it says the tension is 3600 N....
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mqb2766
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#4
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#4
(Original post by TSR360)
In the textbook it says the tension is 3600 N....
The 4 linear forces are 300N each, what are the "distances" used when equating the moments though (sailors <-> string tension). It's basically a "lever-type" question.
Last edited by mqb2766; 1 year ago
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TSR360
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#5
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#5
(Original post by mqb2766)
The 4 linear forces are 300N each, what are the "distances" used when equating the moments though (sailors <-> string tension). It's basically a "lever-type" question.
Sorry, but I'm still confused. What distances are you talking about and how is it a lever-type question?
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mqb2766
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#6
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#6
(Original post by TSR360)
Sorry, but I'm still confused. What distances are you talking about and how is it a lever-type question?
You should be equating moments as you're rotating about a point.
Draw the diagram with the distances and linear forces marked on and upload.
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TSR360
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#7
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#7
(Original post by mqb2766)
You should be equating moments as you're rotating about a point.
Draw the diagram with the distances and linear forces marked on and upload.
I don't know how to draw a diagram like that. The one I have in my w/o is the best I could do.
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mqb2766
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#8
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#8
Missed that. The top diagram is fine.
You have 4 * 300N a distance 1.5m from the centre and a single tension 0.5m from the centre.
So ....
Last edited by mqb2766; 1 year ago
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TSR360
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#9
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#9
(Original post by mqb2766)
Missed that. The top diagram is fine.
You have 4 * 300N a distance 1.5m from the centre and a single tension 0.5m from the centre.
So ....
How does a single tension of 0.5 come from the centre?
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mqb2766
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#10
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#10
(Original post by TSR360)
How does a single tension of 0.5 come from the centre?
The string (linear force, tension) is 0.5m from the centre.
Last edited by mqb2766; 1 year ago
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TSR360
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#11
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#11
(Original post by mqb2766)
The string (linear force, tension) is 0.5m from the centre.
The string goes all the way to the pulley which is at the end of the ship. How can it stop at the capstan?
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mqb2766
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#12
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#12
(Original post by TSR360)
The string goes all the way to the pulley which is at the end of the ship. How can it stop at the capstan?
You're doing the first part?
The cable tension is determined by the capstan. The sailors are pushing with a force 1200N at a perpendicular distance 1.5m. The tension T is at a distance 0.5m. Think of it is a lever where the ratio of the forces is the same as the (inverse) ratio of the distances because the same work is done.
Last edited by mqb2766; 1 year ago
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TSR360
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#13
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#13
(Original post by mqb2766)
You're doing the first part?
The cable tension is determined by the capstan. The sailors are pushing with a force 1200N at a perpendicular distance 1.5m. The tension T is at a distance 0.5m. Think of it is a lever where the ratio of the forces is the same as the (inverse) ratio of the distances because the same work is done.
I still don't understand why the anchor cable's tension is determined by the radius of the capstan. Trying to visualise it as a lever isn't helping either...
Last edited by TSR360; 1 year ago
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mqb2766
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#14
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#14
(Original post by TSR360)
I still don't understand why the anchor cable's tension is determined by the radius of the capstan. Trying to visualise it as a lever isn't helping either...
Do you understand why a lever works (same work done)?
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TSR360
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#15
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#15
(Original post by mqb2766)
Do you understand why a lever works (same work done)?
Yes
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mqb2766
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#16
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#16
Well it's the same. The distance the force is applied over is the circumference of the circle, so proportional to the radius. The sailors apply 1/3 of the force, but do it over 3 times the distance. Or the string tension is 3 times the sailors force as it's applied over 1/3 the distance.
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