Mechanics of Materials - Angle of Torsion

[Femme_physics]

Homework Statement

http://img820.imageshack.us/img820/3373/torsionquestion.jpg

Homework Equations

(In the solution)

The Attempt at a Solution

I got M(max) and d correct. I can't get the angle. But I'm using the formula exactly as is. What's wrong?

http://img209.imageshack.us/img209/5131/torsionanswer.jpg

 

[PhanthomJay]

Max stress occurs in section CD where the moment is 400 N-m, not in AC where the moment is 200 N-m.

You also have the wrong value for Io.

Twist angle at B is the sum of the twist angles of each section.

 

[Femme_physics]

Max stress occurs in section CD where the moment is 400 N-m, not in AC where the moment is 200 N-m.

Fair enough, I miswrote-- but I got the right answer yes?

You also have the wrong value for Io.

Where? I used the right formula according to wiki, to my understanding my answer is wrong because of this ->

Twist angle at B is the sum of the twist angles of each section.

EDIT: Retried it with what I think is your idea...
http://img204.imageshack.us/img204/7044/applying.jpg

Adding the results together does not equate to 1.18 deg

 

[PhanthomJay]

Fair enough, I miswrote-- but I got the right answer yes?

Indeed . Sorry.

Where? I used the right formula according to wiki, to my understanding my answer is wrong because of this ->

My apologies again, you are correct...I was thinking Ix instead of Io.

EDIT: Retried it with what I think is your idea...
http://img204.imageshack.us/img204/7044/applying.jpg

Adding the results together does not equate to 1.18 deg

No, but your method is correct. Remember that the result will be in radians. And don't forget the proper use of your plus and minus signs when doing the addition.

 

[Redbelly98]

Moderator's note: thread moved to "Engineering, Comp Sci, & Technology"

 

[Femme_physics]

Indeed . Sorry.

My apologies again, you are correct...I was thinking Ix instead of Io.

:)

No, but your method is correct. Remember that the result will be in radians. And don't forget the proper use of your plus and minus signs when doing the addition.

Ah...now I see.

Alright, then. I'll give it a crack when I get home today. Thanks!

 

[Femme_physics]

Finally got the result. So this scan is just for the record and to say thank you again...

http://img687.imageshack.us/img687/9876/224na.jpg