Physics Quiz 12

[mastachyra]

Originally Posted by Ether

... 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]

Originally Posted by mastachyra

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:

Originally Posted by mastachyra

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]

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]

Originally Posted by Ether

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]

Originally Posted by mastachyra

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

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]

Originally Posted by mastachyra

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

Close enough. See attachment.