# Can someone help me please... (Integral/Diff. Calculus)

• February 24th 2010, 12:26 AM
Infinity
Can someone help me please... (Integral/Diff. Calculus)
I was reviewing my lessons on our "Strength of Materials" and I came up with this problem.
I get stucked on this thing.
http://img197.imageshack.us/img197/9498/45268362.jpg

How did the final equation/formula came up?
I'm kinda curious.(Doh)(Crying)

help me please!!(Crying) can you explain it to me briefly? and as simple as possible..
thanks a bunch in advance! :D
• February 24th 2010, 02:25 AM
HallsofIvy
$\frac{(0.25)(20\pi)^2}{JG}= \frac{1600\pi^2}{JG}$

I see that there is no "JG" in the last formula. Presumably they have been replaced by some other formula. To get that final expression you must have $JG= 512\pi (0.20)^4(12x 10^6)$.
• February 24th 2010, 03:44 AM
Infinity
that's not what I meant.

I mean. can you explain to me, step by step (if you could) like how did they derive the equation, then integrate. and what are the derivatives that were used if there are.

btw, it's the formula for Torsion in strngth of materials,
theta = angle
J = torsion constant for the section
G = Modulus of elesticity
T = Torsion
L = Length ....