Science & Mathematics - 4 September 2007

and how r they used.........

2007-09-04 08:51:07 · 6 answers · asked by Anonymous in Geography

If the voltage across a device is v(t) = 5cos(10t) V and the current through is i(t) = 0.5sin(10t) A, what is the device power at t = 0.2s and t = 0.4s?

I tried just plugging in the 2 different values, and multiplying them together (p = vi), but that seems too simple.

Is this a problem where I would first have to integrate v(t) and i(t) as well?

Thanks

2007-09-04 08:48:15 · 2 answers · asked by Defcon6 2 in Engineering

what is prime and what is composite

2007-09-04 08:48:11 · 6 answers · asked by Anonymous in Mathematics

I'm looking for a web site that shows you a view of the stars and you can move it about. Doesnt have to be live.

2007-09-04 08:47:53 · 6 answers · asked by Anonymous in Astronomy & Space

intergrate x/(x+1) dx

my answer
= x + 1 - ln(x+1) + C

answer from book:
= x - ln (x+1) + C

2007-09-04 08:44:43 · 5 answers · asked by Snow 1 in Mathematics

An electron has a constant acceleration of +2.2 m/s2. At a certain instant its velocity is +8.8 m/s. What is its velocity (a) 2.4 s earlier and (b) 2.4 s later?

I have no clue what's the difference between 2.4s earlier and 2.4s later

2007-09-04 08:40:26 · 1 answers · asked by Jason N 2 in Physics

275 MA to amps

2007-09-04 08:39:55 · 3 answers · asked by Kelley 1 in Mathematics

to see if they come up with the same answer or to maybe seee if the answer has changed? or maybe to come up with a different answer?

2007-09-04 08:37:00 · 5 answers · asked by Anonymous in Other - Science

2007-09-04 08:34:56 · 12 answers · asked by aniecelinan 2 in Mathematics

I have recently found myself staring at the night sky more and more. I live in central Phoenix, AZ so I understand I still wont be able to see much more with a telescope due to city lights, but how do I find the right one? Right now I am mainly interested in our sister planets, but am sure my interest in other celestial objects will grow once I can actually see them. Thank you!

2007-09-04 08:32:18 · 6 answers · asked by bofay01 1 in Astronomy & Space

Given f(x) and h(x) find g(x) so that f(g(x)) = h(x)

f(x) = x+4
h(x) = 4x-1

So far I have determined that g(x+4) = 4x-1 but am baffled as to how you determine g(x). Seems like a simple problem but I'm having a bit of a problem on it. Please show work!!

2007-09-04 08:25:02 · 9 answers · asked by drew2007 1 in Mathematics

how would i solve this?

2007-09-04 08:23:59 · 10 answers · asked by qt123 1 in Mathematics

i'm looking for a career which involves mathmatics, such as algebra, solving equations, data handling and statistics. i'm wondering if anyone out there knows of any such a job/career. i know it sounds really boring but i realized today that i enjoyed doing all of that at school and was actually really good at it.

2007-09-04 08:23:03 · 3 answers · asked by Anonymous in Mathematics

Is it because during expiremtnats there are always a long process to determine the outcome of the test or what is it?? i dont understand.

2007-09-04 08:22:07 · 4 answers · asked by Anonymous in Earth Sciences & Geology

how do i begin this problem?

2007-09-04 08:16:22 · 1 answers · asked by qt123 1 in Mathematics

2007-09-04 08:15:25 · 3 answers · asked by Toddacanda 5 in Biology

Ok, take the numbers 3, 5, 8 and 10. Use each one only once, and by multiplying, adding, subtracting and dividing....get the answer of 32.

I have tried this 645 ways and still cannot figure it out. I don't know if it's a trick or just very confusing.

Please help asap!
Thanks!

2007-09-04 08:11:00 · 7 answers · asked by echickaboo99 2 in Mathematics

Why?

2007-09-04 08:05:51 · 13 answers · asked by Anonymous in Zoology

Suppose that a boat travels 1 hour downstream and then returns in 1 hour 20 minutes. If the speed of the current is 3 kilometers per hour, find the speed of the boat and the distance it traveled downstream.

2007-09-04 08:05:01 · 3 answers · asked by mistydstephens 1 in Mathematics

What exactly are they teaching kids in high school these days?

I was tutoring a freshman college student recently.
Basic problem: integrate e^(-0.2x) dx
There really is nothing ever so hard about this.

Her first instinct was to pull out her TI89 calculator and do the integration on that. The calculator gave her:
-5*0.81873^x

Clearly since 0.81873 is the evaluation of e^(-0.2), this answer is not wrong, but it's so unintuitive.

Why are students trained to let their calculator do all the work for them? Doesn't anyone do math by hand anymore?

Opinions please.

2007-09-04 08:03:23 · 16 answers · asked by Dr D 7 in Mathematics

2007-09-04 08:00:02 · 7 answers · asked by qt123 1 in Mathematics

Ok guys I asked my apprentice this today and he was able to give me a somewhat decent answer so let's see who the smart ones are out there in yahoo land. How does a capacitor tester get its read ? What does it do to test a capacitor?

2007-09-04 07:58:15 · 3 answers · asked by Jimmy F 3 in Engineering

suppose a is a three dimensional unit vectorin the first octant that starts at the origin and makes angles of 55 degrees and 80degrees with the positive x and y axes respectively. express a in terms of its components.

ok we did a similar example in class and i followed it and used

a=cos55i+cos88j+____k

i got the answer to be <.57, .17, .75> but that is wrong. If you could maybe point out where i went wrong. THanks

2007-09-04 07:57:58 · 1 answers · asked by ♡♥EM♡♥ 4 in Mathematics

1. 2x - 5y = 0 (-2,0), (-10,6), (5,0)

2. 8x - 11y = 0

3. (-7,6) and (0,4); (-9, -3) and (1,5)

4. 4x + 3y = 4

5. The line passes through (-5,6) and is perpendicular to the line that has an x- intercept of 3 and a y- intercept of -9.

2007-09-04 07:54:20 · 3 answers · asked by love_militarymen 1 in Mathematics

What are the ratios of the sides of a right triangle with theta, an acute angle, as one of its angles if cos theta = 25? Please explain your answer. Thanks!

2007-09-04 07:49:39 · 3 answers · asked by sillyboys_trucksare4girls 2 in Mathematics

2007-09-04 07:49:17 · 4 answers · asked by Anonymous in Mathematics

Can anyone prove the following statement? (or falsify it if you don’t believe it?)

b
Σ k * C[M,k] * C[(N-M),(n-k)] / C[N,n] = M*n/N
k=a

a = max (0, n+M-N)
b = min (n, M)

N, M and n are any positive integral constants satisfying
N ≥ M, n (Є Z+)
k (not n) is the index variable.
C[i,j] = iCj = i!/[j!(i-j)!]

NOTE: The limits of the summation, a and b, are only intended to make the nCr function meaningful. k would normally go from 0 to n, but k must never exceed M, and n-k must never exceed N-M.

2007-09-04 07:48:25 · 1 answers · asked by Dr D 7 in Mathematics

A- A new and different set of properties
B- A decrease in the size of the systems
C- A decrease in the number of parts within the system
D- A decrease in the number of energy needed to maintain the system.

2007-09-04 07:47:46 · 3 answers · asked by Anonymous in Physics

Many people know that the weight of an object varies on different planets, but did you know that the weight of an object on earth also varies according to the elevation of the object? In particular, the weight of an object follows this equation:
w = Cr^-2.where C is a constant, and r is the distance that the object is from the center of the earth.

A. Suppose that an object is 100 pounds when it is at sea level. Find the value of C that makes the equation true. (Sea level is 3,963 miles from the center of the earth.)

B. Use the value of C you found in the previous question to determine how much the object would weigh in

i.Death Valley (282 feet below sea level)

ii.The top of Mt McKinley (20,430 feet above sea level)

2007-09-04 07:45:30 · 4 answers · asked by Anonymous in Mathematics

2007-09-04 07:42:07 · 11 answers · asked by Anonymous in Other - Science