PPI Sample Exam Vertical AM problem #5

I'm having trouble getting the answer to match on this one. I think it may have something to do with me missing a conversion somewhere, but I'm not sure.

It's asking for a pressure due to uniformly distributed surcharge load, and I found the equation (AASHTO 3.11.6.2-1) and got all the same angles that the solution presents, however when plugging it in, I keep getting an answer of 0.5172, not 0.90.

I'm convinced I'm missing something very stilly, but I still can't seem to get the answers to line up.

Thanks!

Maybe show your work so we can help you debug... I am getting 0.90.

Make sure you are converting degrees to radians in Eq. 3.11.6.2-1

But for that specific problem, shouldn't you use Eq. 3.11.6.2-3? (for indefinitely long line load). The solution in my book is using that equation.

Hmm, my book is definitely using 3.11.6.2-1 though: DELTAph = 2p/pi (delta - sin(delta)cos(delta+2alpha))

literally plugging in the numbers from the answer into my calculator (HP35s) and I'm getting 0.517.

Breaking it down...

Step 1: 1.292 rad + 2 * 0.785 rad = 2.862 rad

Step 2: cos(2.862 rad) = 0.9988

Step 3: sin(1.292 rad) = 0.0225

Step 4: 0.0225*0.9988 = 0.0225

Step 5: 1.292 rad - 0.0225 = 1.2695

Step 6: 2p/pi = 0.4704

Step 7: 0.4704*1.2695 = 0.5173 (my answer)

I'm guessing I need to do something when using sin/cos and calculating with radians, but I haven't used a radian since who knows when so I'm not sure I'm applying it properly. I'm simply plugging in the number in radians and pressing the cos or sin buttons. Is anyone familiar with HP series calculators seeing something I'm doing wrong?

Thanks all for the help so far

Ahhh! Crisis averted. I have major case of "too much studying brain"...

Just realized I needed to put the 35s into radians mode...hope I don't have such a brain fart on the test!

kalare said:

Ahhh! Crisis averted. I have major case of "too much studying brain"...

Just realized I needed to put the 35s into radians mode...hope I don't have such a brain fart on the test!

Click to expand...

Break time!

Hey SEHQ, can I have you number and if need some help during the test I'll shoot you a text to help me out ?

Hah!

darius said:

Hey SEHQ, can I have you number and if need some help during the test I'll shoot you a text to help me out ?

Click to expand...

Ha! I would give you my number but I don't want you to get in trouble for texting during the exam...