2016 NCEES MD&M - Need help with solution for #536

[aakrusen]

The solution for problem #536 begins by having us use the formula:  µ' = µ(sin(Φ/2)) ÷ (Φ+ sinΦ)  

They help us by making sure we know to convert the angle of 80° to radians,  80° = 1.4rad

But when I put that into the equation, I don't get the same answer the book gets (book has 0.864, I get 0.00686).

Am I doing it wrong or is the book wrong?  I've been wanting to ask this since January but I feel like it's a silly question so I never asked.  It's time to hide the pride and get the help I've been looking for.

 

[JHW 3d]

Can you post question?

 

[Audi Driver P.E.]

Well, 80 degrees is 1.39626 radians.  Without knowing the problem I can't help you much more than that.

 

[J_MEC]

Make sure your calculator is in radian mode.

 

[J_MEC]

Also the equation is wrong and it should be u×(4×sin (phi/2)/(phi+sin (phi))

You are missing a 4 (so is NCEES, but it is a typo) see the MERM page 54-20, equation 54.95 in the 13th edition.

The numerical value of .864 is right of you use the right equation and have your calculator in the right mode.

 

[aakrusen]

Also the equation is wrong and it should be u×(4×sin (phi/2)/(phi+sin (phi))

You are missing a 4 (so is NCEES, but it is a typo) see the MERM page 54-20, equation 54.95 in the 13th edition.

The numerical value of .864 is right of you use the right equation and have your calculator in the right mode.

MEC, Thank you!!  Also, thank you for the reminder about setting my Calc to Rad instead of Deg.

 

[J_MEC]

No problem, you're welcome. The calculator/radians thing you gotta be careful with. Don't want to live this meme!

I am heading to bed (on the east coast). Good luck tomorrow! I hope we both pass!

View attachment 9362