Chief Delphi - Physics Quiz 12

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- Math and Science (http://www.chiefdelphi.com/forums/forumdisplay.php?f=70)

- - Physics Quiz 12 (http://www.chiefdelphi.com/forums/showthread.php?t=145068)

mastachyra

15-03-2016 20:49

Re: Physics Quiz 12

Quote:

Originally Posted by Ether (Post 1557774)

... and the force on the D roller is downward (perpendicular to the rail)

Double-check that 632N number.

Whoops, thanks for clarifying the direction. Of course the force can only be down on the roller...

But I can't find the issue with 632N. The left over torque is -948 N*m and the torque arm from A to D is 1.5 m. no?

Ether

15-03-2016 21:32

Re: Physics Quiz 12

Quote:

Originally Posted by mastachyra (Post 1557959)

But I can't find the issue with 632N. The left over torque is -948 N*m and the torque arm from A to D is 1.5 m. no?

Where did you get this from:

Quote:

Originally Posted by mastachyra (Post 1557699)

the torque arm for the tension is 1.0 meter, which is found by extending the force vector backwards until a perpendicular line crosses through point A.

mastachyra

15-03-2016 22:27

Re: Physics Quiz 12

http://i.imgur.com/IU70nhu.jpg?1

OK, I see the error of my ways. I started from scratch (instead of trusting previous answers) and cleaned up my work to make deciphering a bit easier. I didn't bother with significant figures. New answer:

Part a) Tension on cable is 5454 N.
Part b) Force is 16082 N up on roller A and 291 N down on roller D.

I hope this is correct... mostly so we can get a new problem to work on!

mastachyra

15-03-2016 22:43

Re: Physics Quiz 12

Quote:

Originally Posted by Ether (Post 1557982)

Where did you get this from:

Oh, you switched your question on me. I did things differently in my new answer, using the components instead of the actual tension on the cable. The 1.0 m torque arm was derived with the geometry that is circled and labeled TENSION TORQUE ARM. It's pretty crude, but I think it checks out. Here's clearer work on that part:
http://i.imgur.com/RCNAGre.jpg?1

mastachyra

15-03-2016 22:46

Re: Physics Quiz 12

Quote:

Originally Posted by mastachyra (Post 1558031)

and i just caught the mistake in that too... the 8 degree angle should be 12. Which makes the 36 degree angle 40, and the torque arm, x = 1.1 m.

Ether

15-03-2016 23:08

Re: Physics Quiz 12

1 Attachment(s)

Quote:

Originally Posted by mastachyra (Post 1558019)

I hope this is correct... mostly so we can get a new problem to work on!

Close enough. See attachment.

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