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1. ### Difference and summing OP AMP

so even though this is a part summer, part difference amplifier, the method we used will apply? anyway, thanks a lot for your help berkeman, this problem was giving me nightmares last night..
2. ### Difference and summing OP AMP

what confuses me is that why can't the current i_1= 1/2k, i_2=.25/3k, i_3=.75/5k for the currents entering v_i+? also would the current into the node with the two 4k resistors be 2/4k + 0-v_i-/4k?
3. ### Difference and summing OP AMP

heres another shot: ((1-v_i+)/2000) + ((.25-v_i+)/(3000)) + ((.75-v_i+)/5000)) = 0 v_i+=.7097 v_o-=v_i+ ((v_o- - .7097)/(50000)) + ((1-.7097)/(2000)) + ((2-.7097)/(4000)) + ((0-.7097)/(4000))=0 v_o-=-13.81
4. ### Difference and summing OP AMP

ok so from what i understand from what you said, here is what i have done: .067/2000 + 2/4000 + -2/4000 + ((2-v_o)/50000) = 1/2000 + 0.25/3000 + 0.75/5000 then i solve for v_o? does that look correct?
5. ### Difference and summing OP AMP

IDEAL CHARACTERISTICS: A_ol=inf R_i=inf R_o=0 i_+=0 i_-=0 v_in=v_+ - v_- v_out=A_ol(v_+ - v_-) v_+=v_- but i don't see how any of them would make this problem easier
6. ### Difference and summing OP AMP

the "1",".25",".75",".67", and "2" are all voltages. are you saying that i should right nodal equations for the inputs? i didnt quite understand what you meant...
7. ### Difference and summing OP AMP

hey guys, i have a HW problem of a combination of a summing and difference op amp. I got the first few steps of the problem, but i don't know how to continue from where i am. I am having a hard time solving for v_+. any help is greatly appreciatd, maybe if you guys can not solve the problem for...
8. ### Fourier transform of x(t)=u(t)-u(t-1)

Im trying to get the Fourier transform of x(t)=u(t)-u(t-1) from what i know the FT of u(t) is pi*delta(omega)+1/jw so for the u(t-1) would we have to use the time shifting property of Fourier transforms so that it becomes pi*delta(omega)+1/jw*(exp(-jw_o)??
9. ### Finding Frequency of 20mH Inductor & 30 Ohm Resistor in Parallel

im given a a 20-mH inductor and a 30 ohm resistor in parallel. Z_in is 25 degrees. and I am asked to find the frequency omega in rad/s here's what i try to do: 25=(jw.02*30)/(jw.02+30), and solve for w, but i don't get the right answer. what is it that I am doing wrong?

Im having trouble comparing sinusoidal waves and their phases. As a sample problem I was given v_1=120cos(120*pi*t - 40deg) and i_1=2.5cos(120*pi*t +20deg) and I was asked to find the angle by which i_1 lags v_1. I have no clue on how to go through with this problem, I don't even know...
11. ### Thevenin Equivalent: HW Problem Solution Check

you may be right about the load resistor lying betwen the two points. But even if i don't remove the load resistor, and use the same technique to find V_AB, then id still have the same equations because there would still be no current through the 10k resistor.
12. ### Thevenin Equivalent: HW Problem Solution Check

GREAT! thanks teknodude!
13. ### Thevenin Equivalent: HW Problem Solution Check

if you look at the second circuit i have labeled the two nodes V_A and V_AB, those are the two nodes in which i am going to do nodal analysis in.
14. ### Thevenin Equivalent: HW Problem Solution Check

i have an attempted solution to a HW problem, and I want to know if it is right or wrong. Could you guys please help me out. I have attached the image as a pdf
15. ### Solving an Electrical Problem: 79.2V Answer

ok here's the URL of the work [img=http://www.freeimagehosting.net/uploads/th.d669771024.jpg] http://www.freeimagehosting.net/d669771024.jpg [img=http://www.freeimagehosting.net/uploads/d669771024.jpg] theres a bunch of links to the image, this is my first time using this imageshack thing...
16. ### Solving an Electrical Problem: 79.2V Answer

hello. I was reading through the chapter, and i came across a practice problem. The given answer for the problem is 79.2V. I attemted to solve it, but i don't get the same answer. ICould you guys please help me out and tell me where i am making a mistake? Thanx in advance...
17. ### Determine sources being charged

its ok, I am just going to wait until the professor goes over the answer in class today. i mean that's the circuit the book has given us, so that's what I've been trying to work on. thanks for your help tho
18. ### Determine sources being charged

ya, I am positive that the circuit is drawn correctly, i just copied it straight out of the book...
19. ### Determine sources being charged

i keep getting stuck in this problem, i don't see what I am doing wrong. the problem says to determine which sources absorb positive power, then show that algebraic sum of the five absorbed power values is zero. i have attached a picture of the circuit, and here is what i have done: Starting...
20. ### Good book for me to review general math

Can anyone recommend a good book for me to review general math such as fractions, decimals, percenttages, and division etc.. those are my weakest points in math, and I would like to strenghten them a bit.
21. ### Series solution near an ordinary point

the polynomial is not going to look like the other ones?
22. ### Series solution near an ordinary point

why was it necessary for you to set x= 1+(x-1)
23. ### Series solution near an ordinary point

we know that y'= \sum_{n=0}^{\infty} n a_{n} (x-1)^{n-1} y"= \sum_{n=0}^{\infty} n (n-1) a_{n} (x-1)^{n-2} when we compute xy', doesn't it become just: \sum_{n=0}^{\infty} n a_{n} (x-1)^{n} ? i don't see how \sum_{n=0}^{\infty} n a_{n} (x-1)^{n} and - \sum_{n=0}^{\infty} (n+1) a_{n+1}...
24. ### Series solution near an ordinary point

oh wait nvm my last post, i got it, thank you.
25. ### Series solution near an ordinary point

i don't understand how you got the -(x-1)y'. does the term xy' change to (x-1)y' when the x in the y=SUM an(x-1)^n changes also? I am sorry, but is there a way you can show you got the 2nd and 3rd summation in your solution in more detail please?
26. ### Series solution near an ordinary point

Im given y"-xy'-y=0 at x0=1. The problem asks for recurrene relation, and the first four terms in each of two linearly independant solutions, and the general term in each solution. Whats thrwoing me off is the x0=1. I tried doing y= SUM an(x-1)^n, but when i differenetiate and plug in, i get...
27. ### Programming questions

Can i post programming questions in the Homework help section?
28. ### Material science-Specification of composition

it is that book, but it is in chapter 5, not chapter 4.
29. ### Material science-Specification of composition

Im given this problem: Ge forms a substitutional solid solution with Si. find the weight% of Ge, that must be added to Si to yield an alloy that contains 2.43x10^21 Ge atoms per cubic centimetr. The densities of pure Ge and Si are 5.32 and 2.33 g/cm^3, respectively. then I have a formula...
30. ### Spherical coordinates angles of phi

for example I am given a triple integral for the function w=z outermost integral is: the integral from -2 to 2, dx middle integral is: the integral from -sqrt(4-x^2) to sqrt(4-x^2), dy and inner most integral is: the integral from x^+y^2 to 4 they say to convert this to spherical...
31. ### Spherical coordinates angles of phi

im having trouble determining the angles of phi in spherical coordinates when asked to convert a triple integral into spherical, and find the limits of the phi integral. can anybody point out any hints/tips/tricks how this may be done??Please...i have an exam tomorrow and I am tryn to prepare...
32. ### Setup Double integral

thanks, i get it now. that was a tricky problem...
33. ### Setup Double integral

thanx for tryn Benny, but unfortanately the answer you gave was incorrect. the way the book does it is like this: inner integral= sqrt(1-x^2)dy,0,x outer integals limits are 0-1, dx and the entire integral multiplied by two. the final answer is 2/3 the equation they gave for the xy...
34. ### Setup Double integral

i have to setup a doble integral to find the volume of the solid bounded by the graphs of the equation. x^2+z^2=1, and y^2+z^2=1 z=sqrt(1-x^2) z=sqrt(1-y^2) then substituting in z=sqrt(1-y^2) into x^2+z^2=1, i got y=x. so when i setup a double integral for the dy i get integral...
35. ### Annoying integral

gotcha, thanx.
36. ### Annoying integral

so make the u=2x+1 substitution in the first step of the problm?
37. ### Annoying integral

Hey guys i keep getting stuck with this: integral of ( ln(2x+1)dx) im supposed to use by parts heres what i have done u=ln(2x+1) du=2/2x+1 dv=dx v=x then i apply the formula uv-vdu and i end up with another integral I am supposed to use by parts for: integral of(2x/2x+1 dx) heres...
38. ### Thermal energy(physics)

A 1500 kg car traveling at 20m/s skids to a halt. What is the change in the thermal energy of the car and the road surface? Here is how i try to approach it but i get a wrong answer: First I solve for All dissipstive forces which is the frictional force in this problem. I said the...
39. ### Converges or diverges

just a thought, wouldn't the limit comparison test work on this if you choose your b_n to be 1/n, and use the p-series to say b_n diverges?
40. ### Molarity homework problem

200 ml of a 6 M HCl solution is added to 400ml of a 1.50 M HCl solution. find the concentration of the mixture. here is what I think should be done: (6M)(V concentration)=(.8L)(1.50M) can i add the two volumes together? Is this correct?
41. ### What is the minimum mass m that will stick and not slip?

a block of mass m is resting on a 20degree slope. The block has coefficients of friction mu_s =0.80 and mu_k =0.50 with the surface. It is connected via a massless string over a massless, frictionless pulley to a hanging block of mass 2.0 kg. (sorry didnt know of a way to distribute a picture)...
42. ### For Part A: Find Limiting Reactant of 2.70g Al & 4.05g Cl2

2Al+3Cl2=Al2Cl6 a)which reactant is limiting if 2.70g Al and 4.05g Cl3 is mixed. b)what mass of Al2Cl3 can be produced. for part a i found the limiting reactant to be Cl2. I don't understand what I am supposed to do for the second part. Should i write another equation as Al2Cl3 as the...
43. ### Fictituous forces and apparent weight

how would i find the speed of the car at the bottom?
44. ### Fictituous forces and apparent weight

The passengers in a roller coaster car feel 50% heavier than their true weight as the car goes through a dip with a 30.0 radius of curvature.
45. ### Velocity in uniform circular motion

sorry, that was a thoughtless question which i realized afterwards. thank you :blushing:
46. ### Quick conversion ?

ok. the first part of the problem asked me to find the tension in the string. to do that i used Newtons second law where Tcos(theta)=mg to find theta, i looksed at the picture, and since the radius(opposite side of the angle) and the hypotenuse were given, i applied sin, which was...
47. ### Quick conversion ?

A conical pendulum is formed by attaching a 0.100kg ball to a 1.00m-long string, then allowing the mass to move in a horizontal circle of radius 40.0cm. What is the ball's angular velocity, in rpm? from using sin, i obtained 23.57 degress. I am not sure how i would convert that to rpm
48. ### Quick conversion ?

how would i convert 23 degrees to revolutions per minute
49. ### Velocity in uniform circular motion

hey bro how did you get the T=86400 sec? thanks for your help, it was the correct answer!
50. ### Velocity in uniform circular motion

A 300-m tall tower is built on the equator. How much faster does a point at the top of the tower move than a point at the bottom?