Challenge Definition and 942 Threads

Hello, With regards to a Youtube video- Spin polarized tunneling - video #10: , could some one familiar with electronics provide a circuit or diagram for this to work? Also what type & size of barrier could be used? This should be fairly easy for anyone familiar with electronics, so any help...

Homework Statement The problem is If x= 2+2 2/3 +2 1/3 solve x 3-6x 2+ 6x-2 =0 Homework Equations The Attempt at a Solution First i tried to substitute the values but its turning out to be really big( and i get quite scared when it turns up like this and so i didn't go any further...

NEEDD HELP! parameterizing a surface given by an implicit function (HYPERBOLOID?!) Homework Statement I need to parameterize the surface given by the following implicit equation: x2 + y2 + z2 + 2xy + 2xz - 2yz = 1 Homework Equations I tried using all sorts of subsititutions...

This isn't a homework question or anything, but I came across this challenge problem posted on a Harvard Math 25a webpage and I'm wondering what the solution to it is since no solution is posted on the page. Suppose that f\colon \mathbb{Q} \to \mathbb{Q} satisfies f'(x) = f(x) for all x \in...

Homework Statement Determine the force P required to like the 200kg crate. Coeff. Static friciton is 0.3 on ALL contact of surfaces. Neglect Wedge Mass Homework Equations μS x Fn = Fk Summation of forces eqns The Attempt at a Solution im getting more unknowns than equations see attachment.

Solid Mechanics questions - A new challenge :) Hi all :wink: I got 3 new questions that need to be solved in about 3-4 days as part of a 'challenge' homework. Those who solve correctly will basically get their names read out loud on the next lecture but I do it to understand the material of...

Homework Statement Two moons orbit a planet in nearly circular orbits. Moon A has orbital radius r, and moon B has orbital radius 5r. Moon A takes 50 days to complete one orbit. How long does it take moon B to complete and orbit? Homework Equations Kepler's Third Law The...

hi everyone ! we have two circles that doesn't have intersections now we want to find a point on each circle that the distance of this two points are 'k' please help me . . .

hi :] i have a surprise for anyone who can solve my challenge: we have the korona voltage formula... http://img130.imageshack.us/img130/4859/aaae.jpg" let's see who can give me the long way to it (from beginning to end and can explain it).. since it's the final formula.. only 3...

I'm currently trying to write a report at the moment with some tables for some data, and it would be ideal for me to put these tables side-by-side if possible. However, I'm not sure as to how this can be achieved; I've currently doing \documentclass{article} with multiple figures of graphs...

Hey. Im currently doing a course in numerical analysis, and while most of the focus is on the mathematics side of things, the assignments are set in an engineering context. One of my assignments describes a beam that is "pin jointed" at both ends, is 1 meter long, and is subject to a 0.5 N/m...

Sled Dogs work? A team of dogs drags a 46.5 kg sled 1.73 km over a horizontal surface at a constant speed. The coefficient of friction between the sled and the snow is 0.233. The acceleration of gravity is 9.8 m/s2 . Find the work done by the dogs. Answer in units of kJ [b]2. W=Fd F=mg...

Can you give me a suggestion how to find a reasonable algorithm do distribute undividable goods among different people? All of the people have different preferences, but might be clashing. Also some of them might have priorities, due to not getting anything last round. So for one round there...

Pi. An infinite number. INFINITE. People have been memorizing the digits of pi to a certain number of decimal places. A challenge for you: how many can YOU remember? I hold the world age record(i actually don't, because i haven't told anyone except my friends about it) for memorizing 1500...

Insane Electromagnetic Induction Question. Challenge your brains! :D F=BIL, F=mg There is a B field acting on the rod so we resolve that. I tried to resolve the other force vectors according to: 1. Force acting on rod by gravity 2. Force acting on rod by electromagnetic (F=...

Greatest challenge for science-- Reincarnation! I don't know about other European countries but Here in south-east-Asian country, more definitely, India and Nepal, We have a bunch of stories regarding re-incarnation or rebirth. There are lots of evidence that a boy/girl only 3 or 4 years old...

"It's the planet that really shouldn't exist – or at least not for long. It is 10 times the size of Jupiter, orbits its own star in under 24 hours and should soon be spiralling into the surface of its searingly-hot sun..." Full story...

PHYSICS...please help! Four astronauts are in a spherical space station. 1) If, as is typical, each of them breathes about 500cm^3 of air with each breath, approximately what volume of air (in cubic meters) do these astronauts breathe in a year? 2) What would the diameter (in meters) of...

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Homework Statement We all know the egg drop, and I am stuck as to what to do with the extreme little amount of materials we are allowed to use. Here they are: 1 regular supermarket egg 5 sheets of printer paper 1m of scotch tape We are to drop it once from the ceiling of our...

I am working with 2 by 2 matrices, L, X, P and T. L = PTP -------Eqn 1 X = PTTTTTTP ----------Eqn 2 where L and X are known matrices. P and T matrix are unknown and are to be solved. The above problem looks simple but are you able to solve it?

Lets do this: http://www.freetetris.org/ My high score so far: 65,324

Hello ! My friend challenged me to remove a sheet that is under a standing pen, without the pen falling. I can only use 2 finger and i can only touch the paper. Do you know a way to do this ? (he said that I have to use physics)

Egg Drop Design Help! 1. Ok, I need some ideas for an egg drop project in my class. A. Dropping from 7 Ft, then 12 Ft, and then 25 Ft... Consecutively. B. Can't be more then a Meter in height. C. Allowed to use the following: 1. 15 Popsicle Sticks 2. 15 Straws...

I have an electrical engineering question for all you electrical engineers! If I have multiple motors in series, there will be a voltage drop due to the internal resistance of the motors. What will this look like for the motors? Will each motor experience a different voltage or will the...

Space Elevator Your first job after graduation you are hired by a engineering firm that just got a contract to build the first space elevator. The space elevator consists of a cable hanging from geo-stationary satellite to an anchor point on earth’s surface. Once installed this equipment can...

Hello this is my first time here. I would like to ask some question regarding the competition that my schoool is going to enter. It is called the F1inschool challenge. We are asked to design a F1 car powered by a CO2 cannister. I am having a dilemma here on wheter to increase down force or...

Can anyone take up this challenge?

I am a registered contestant in the M-Prize Competition. The Competition was started by top scientific professor's and the purpose of the competition is to design a spacecraft that can travel to an altitude minimum of 100km and orbit Earth 9 times or more, in addition to that the whole...

Hi, i have just registered to the forum, because this time i study number theory and in some problems i can't figure out how to solve them. This time i have to prove: If two integers x,y doesn't divided with 3 then the (x^2 - y^2) always is divided with 3. Does anyone has a clue how to...

I'm not sure how you apply the rules of a derivative on a quadratic form. I've been trying to find the solution on google but no luck: Basicallly: J=\frac{1}{2} (z-X \theta)^T (z-X \theta) and \frac{ \partial J}{\partial \theta}= -X^T z +X^TX\theta I can't for the life of me...

Homework Statement A submersible with a mass of 2.75 x10^3 kg remains at a constant depth beneath the ocean surface. To make the submersible rise, 1.50 x10^2 kg of ballast is released. Ignoring friction, what is the upward acceleration of the submersible? (D = 1.025 x 10 ^3 kg/m^3 )...

Homework Statement I'm given a chart of Force vs Seperation with the following values: SEPARATION (m) 0.1 0.2 0.3 0.4 0.5 0.6 FORCE (N) 0.79 0.48 0.20 0.05 0.022 Where FORCE is the y-axis, and 0.1 corresponds with 0.79. I am not given any other values. All I know is...

Hello, to understand the renormalization of phi^4 theory, I read Peskin Schröder and Ryder. In both books important steps are left out. I found the following identity in Peskin Schöder "An Introduction to Quantum Field Theory" on page page 808, equation A.52 (Appendix) \frac{\Gamma(2 -...

Homework Statement What is \int_0^{2 \pi} \; d\theta \sin^2 k\theta \cos^2 k\theta \; ? Homework Equations Orthogonality of sines and cosines? The Attempt at a Solution I tried substitution and didn't get anywhere. Yeah, that's about it.

Please consider this simple, but very interesting interpretation of the nature of space in special relativity. Space is both relative AND absolute. Why? Let's take a very simple example. The Eiffel Tower is 10,000 miles East from City X and 2,000 miles East from City Y. Michael is in City...

Homework Statement use five fours ONLY to get 44 Homework Equations The Attempt at a Solution

Can anyone name for me: a] a material that has a HIGH electron affinity and is a GOOD conductor of electricity. b] a material that has a MID-RANGE electron affinity and is a POOR conductor of electricity. c] a material that has a LOW electron affinity and is a GOOD conductor of...

[b]1. You plan a trip on which you want to average 90 km/hr. You cover the first half of the distance at an average speed of only 48 km/hr. What must your average speed be in the second half of the trip to meet your goal? Note that the velocities are based on half the distance, not half the...

Homework Statement i need help in solving this,coz i have an exam tomorrow,please help me,i search everywhere and i didnt know how to do it Homework Equations find the curvature of the fowloing curve r(t)= t i +t^3/2 j , t>0 The Attempt at a Solution

Kerr black holes have 2 horizons: outer (event horizon) and inner (cauchy horizon). I also heard that inner horizon is called a Killing horizon, which is actually funny because it can KILL - literally. Even it is not proven yet, but it is possible that there is an infinite density of evergy...

Homework Statement Homework Equations The Attempt at a Solution Homework Statement Homework Equations u = 1+tant du = sec^2(t) dt dt = du / sec^2(t) The Attempt at a Solution It seems like I should be using substitution in the equation, however the exponent is...

It's February, and http://my.funtrivia.com/private/main.cfm?tid=87626". Check out the trivia sticky at the top of this page for the link after this thread disappears. The competition is month to month, with monthly winners kept in the "hall of fame." It requires a simple registration (no...

Homework Statement Find the volume enclosed between the by the cylinder x^2 + y^2 = 2ax and z^{2} = 2ax Homework Equations The Attempt at a Solution The problem can be done by evaluating the triple integral \int \int \int dxdydz , but i am not able to visualise how the second...

Homework Statement Prove these propositions Homework Equations If x is rational, then x + sqrt(2) is irrational. If x + sqrt(2) is irrational, then x is rational. If xsqrt(2) is irrational, then x is rational. The Attempt at a Solution I've tried a couple of ways, but I always end...

Okay, I have been wondering this for a long time. The question concerns buoyancy of objects in water. Question: Imagine you have a balloon filled with air. Imagine the balloon has virtually zero mass, but actually has a virtually infinite hardness. You could replace the balloon with a force...

I'm studying for an exam and can't seem to get this last practice problem! I've tried many ways but still keep getting the wrong answer. The professor has already given us the correct answer to the problems, but I want to know HOW to do it for the exam! Thanks in advance :) A boat radioed a...

Homework Statement Consider the circle D on the plane with the center (2,0) and radius r=1. Revolving D about the y-axis, we obtain a donut (torus). What is the volume of this donut? Homework Equations Assume: F(x)=\int^{a}_{-a} sqrt(a^2-u^2)du = (PI * a^2 )/2 where a\geq0...

proof! god do i hate these things, ok here we go, A------------B------------------------C P------------Q------------------------R Given:ABC, PQR, AB=PQ, BC=QR Prove:AC=PRThe Attempt at a Solution statements/Reasons 1.ABC and PQR/Given 2.AB=PQ and BC=QR/Given 3.AB+BC=PQ+QR/All lines are...

Homework Statement A dog wishes to swim across a slow-moving stream. The dog can swim at 2 m/s in calm water. The current velocity is 3 m/s. The distance directly across the stream is 50 m. If the dog points himself directly across the stream how long will it take to get across the...