Challenge Definition and 911 Threads

Bob owns a couple of hourglasses -- one is a 4 minute hourglass and the other is a 7 minute hourglass. If Bob wants to measure 9 minutes, how could he do it?

I tutor an AP Calculus AB class at the library every week, and I recently gave the students a test on Limits and Continuity. The test was fairly straightforward, but some of the free-response questions were somewhat difficult. The students seemed to get the answers fine, but my friend/mentor...

Following is a non-peer reviewed journalism. Is there merit to this? http://www.voanews.com/english/news/science-technology/600-Million-Year-Old-Microscopic-Fossils-Upend-Evolution-Theory-136172283.html

Given polynomials of degree n > 2, such that they have the form of p(x) \ = \ x^n \ + \ a_1x^{n - 1} \ + \ a_2x^{n - 2} \ + \ a_3x^{n - 3} \ + \ ... \ + \ a_{n - 2}x^2 \ + \ a_{n - 1}x \ + \ a_n. And \ \ all \ \ of \ \ the \ \ a_i \ \ are \ nonzero \ integers \ (which...

What are the domain and range of the following: (Note: It is a relation that is not a function.) y^2(x^2 - 1) = x^4

Homework Statement The egg protecting device cannot slow down the natural descent of the egg in any form: The mechanism used to protect the egg cannot rely on buoyancy (i.e. no inflated balloon-based solutions) or air resistance (i.e. no parachutes or solutions designed to increase the air...

Homework Statement i have just learned that one mole is actually what i had learned as one molecule. now one atom is also known as one mole.eg. one mole of methane has 5 moles of atoms( this sentence is written by my teacher and no matter how i try to look at it from different perspectives...

So I was given a challenge problem in physics class that reads... Mass m1=40kg, is sitting on a frictionless floor while m2=10kg sits on top of it. Between each mass, the coefficient of static friction is .6, and the kinetic coefficient is .4. M2 is pulled by a force of 100N to the left. What...

Solve showing full working (x^2 -1)y' + 2xy = x You must show full working.

Homework Statement Integrate the following: (sin(x)/x)^4 between negative infinity and infinity. Homework Equations The residue theorem, contour integral techniques. The answer should be 2pi/3 The Attempt at a Solution I'm not even sure where to start honestly. I define a function...

Any help on this quistion would be greatly appreciated. I have no idea ho to answere it, and can't find anything in my nothes or books anywhere. The temperature-dependent molar specific heat capacity at constant pressure of many substances is given by: c =a+2bT−cT^−2 For magnesium, the...

I've been working on a multi-latteral project lately with afew of my collegues where our end goal is, free, wireless energy. The process is nearly complete and we hope to be able to broadcast this energy on a global scale, most of our technical issues have been worked out over the years but one...

Homework Statement The question is on the attached picture, it's question number 2! Homework Equations Dealing with pulleys The Attempt at a Solution

Homework Statement A plane flies at 900m and has to deliver a package. It flies at 180 m/s North at 15° below the horizontal. The ships velocity is 40 m/s and it is traveling due north. At what horizontal distance from the ship must the package be dropped for it to land on the ship?Homework...

Hi forum, Here is a little challenge that I came up with that some of you may find interesting:- Using only a compass, ruler and pencil, can you draw a circle, of any diameter you wish, and divide its circumference exactly into 360 equal sections? It seems to me that one should be able to...

Homework Statement The object of the lab is to find the diameter of the bouncing ball shown in the pdf attached. We are working with Logger Pro. The only 2 pieces of information that we have is that the ball is on the surface of the earth, where Ay=-9.81 m/s2, and that the frames are 0.05...

"Speed-of-light experiments yield baffling result at LHC" - 22nd Sept News Article?! http://www.bbc.co.uk/news/science-environment-15017484 Came here to get some further information and I can't find a thread. If there already is one about this, sorry I should delete it. Very interesting...

My Siphon Challenge FINALLY! I've thought over my remarks concerning the theory by Dr. Stephen Hughes, Lecturer in Physics at Queensland University of Technology, concerning gravity, rather than differential air pressure, as being the primary source of motive energy for a siphon system. (See...

Hello, all. My colleagues and I are currently working on an exercise book for The Feynman Lectures on Physics (FLP). This book will include about 1000 exercises from the original Feynman Lectures course as taught at Caltech, covering pretty much the entire range of topics in all three volumes...

Hello. I've got an idea to build a plot in real time. What i want to do: 1) I've got a row (array) of numbers 2) for these numbers i calculate values of the expression i want to plot, put them into array, 3) use list plot or smth like that with the row and the array. The question is : how...

Hello all... I have been working on this problem that I just am not being able to solve. I've been spending my spare time learning some vector calculus and non-euclidean geometry (my aim is to be able to finally tackle relativity). After learning some basic things about the del function, I...

Hi Physics Forumers! I was listenining to the Feynman lectures and something Feynman said got me thinking. He was talking about the indeterminacy that exists in classical physics due to our uncertainty in the initial conditions: I was wondering how he derived this. So I thought I would turn...

Some of my friends, upon finding out that I'd joined these forums, decided to give me a math challenge problem they thought couldn't be solved. Does everyone get the same answer? It goes as follows: A knight jumps on a chess board (assume it makes a legal move) from point A to point B...

***Fun Challenge -- weighted average of global rankings*** Goal The goal is to create a weighted average of global rankings. Does not have to be perfectly accurate (if that was even possible). Specific Example To make this problem less abstract and easier, we are going to use a specific...

http://www.esa.int/esaCP/SEM5B34TBPG_index_0.html "ESA’s Integral gamma-ray observatory has provided results that will dramatically affect the search for physics beyond Einstein. It has shown that any underlying quantum ‘graininess’ of space must be at much smaller scales than previously...

Hey guys, its me again! This time, I was reading about projectile motion in my textbook, and noticed that they didn't prove some of the claims presented about this topic. So I decided to try and prove it myself as a challenge. I included it here as a PDF. It's a pretty short and simple proof...

Homework Statement http://img691.imageshack.us/img691/8826/problem14.jpg The Attempt at a Solution I don't know where to begin... My attempt isn't even worth putting up..

I understand why liquid is sucked into a tube of flowing air with a constricted end due to Bernoulli's principle, what puzzles me is why the air doesn't just take the path of least resistance instead of inducing liquid suction (see attached image). For example, if a 1/4 inch line at 30 psi has...

Here's a nice problem: Prove that \frac{k!}{k^k} \leq \frac{(k-j)!}{(k-j)^{k-j}} \frac{j!}{j^j} for all natural numbers such that 0\leq j\leq k. (Convention: 0^0=1.) I proved this myself, so I'm not asking for help any more. I merely decided to mention this problem to those of you who seek...

Hi all, I have read this forum on and off for a couple years' now and have finally started the road to calculus. I have a BA in Econ already (2001) and took the "Business Calc" class way back (that's what the minimum was). I find myself in a technical career (not Econ related), but have...

This is a challenge problem I received in my calculus class that I believe uses math lower than Calculus. My worry is that the way I want to solve it seems too simple. Homework Statement A long hallway contains lockers numbered 1 through 1000. At the start of the day, all of the lockers are...

This is a fun question I found and wanted to share. Please, do not bother to tell me that I need to post equations or show my attempt as I have solved it myself. As I liked this question I am sharing it on PF. Here it goes: There are 2011 points randomly chosen and a resistance R is...

Hi all, I've attached a challenge problem I've been working on and have been running into some trouble... Thanks in advance.

This really doesn't have anything to do with what most of you are familiar with, but I'd probably peg you guys above average in intelligence relative to other forums so I thought I'd give it a shot. I had a pretty good GPA and above average SAT scores coming out of high school that enabled me...

Pringles "100 Crisps" Challenge If you look on a can of Pringles, it says "100 Crisps In Every Can, On Average" Here's a challenge for you all (if you guys are up to it): Buy at least 2 cans of Pringles. Count the number of Pringles in each can, then post those results. EDIT: To clarify...

I am looking for extremely challenging math equations/problems to solve. I would appreciate any problems in any field of mathematics (almost nothing is too difficult). Note that I am looking for straightforward problems with an answer (not proving someone else's conjectures). Who knows, others...

.. As I read the situation, DrChinese frequently challenges local realists -- of whatever hue -- here, in the Quantum Physics section of PF. As I understand the details: The challenge is delivered in the context of Aspect's experiment, the twinned photons are identically correlated (in the...

Hello, I am faced with a perplexing challenge in analyzing my results for an ecology experiment. All help is immensely appreciated. The situation: I have 6-month longitudinal mass data for 8 hummingbirds. From eye-balling the data, time definitely has an effect: masses tend to decrease...

This isn't even for the campus where I go to school, but as an amateur astronomer, I feel that this message should be spread everywhere. http://www.tdgogreenchallenge.com/video/p/1/playid/149/id/149/ Light pollution is something more than a nuisance to astronomers, it is also something that is...

Homework Statement A massless spring of constant k=78.4 N/m is fixed on the left side of a level track. A block of mass m=0.50-kg is pressed against the spring and compresses it a distance d from equalibrium position B to a compressed position A. The block, initially at rest, is then released...

I have a problem with calculating the concentration gradiant. Here is the question and the solution from the solution manual and the numbers don't add up. A 1-mm sheet of FCC iron is used to contain nitrogen in a heat exchanger at 1200℃. The concentration of N at one surface is 0.04 atomic...

Some matter (non-empty waves) formed a Black Hole. Black Hole emits Hawking Radiation. After a while, Black Hole dissapears, and there is nothing but radiation going in all directions. My question, How 'guided particled' managed to escape from the Black hole? Or, if they did not escape...

Homework Statement \sum_{k=0}^{4}\cos^2\left({\frac{2\pi k}{5}\right) = 5/2 The Attempt at a Solution I have to prove that. I don't know how. Maple gives 1+2*cos((2/5)*Pi)^2+2*cos((1/5)*Pi)^2 evaluated numerically it is equal to 2.499999. But I don't remember the trick to doing this...

Homework Statement I have to find all the partial limits {I hope this is how this term named in English} of a sequencesHomework Equations a_1=0 a_{2n}=\frac {a_{2n-1}} {3} a_{2n+1} = 1/3 + a_{2n} The Attempt at a Solution I have tried to prove first that sequences of all the even terms...

I'm looking for a formula to represent the idea that if I didn't have you, someone else would be equally nice or better. Suggestions? Thanks, Dian

Homework Statement Let I be an interval, and f: I --> R be a continuous function that is known to be differentiable on I except at c. Assume that f ' : I \ {c} --> R admits a continuous continuation to c (lim x -> c f ' exists). Show that f is in fact also differentiable at x and f ' (c) =...

In my engineering class, we were told to create a structure out of balsa wood (1/8"x1/8") and glue. The structure has to suport the weight of 3 15lbs. weights (donut shape). We are only give 72" of balsa wood, and the structure must hold the 3 15lbs. weights for 1min. Sorry I am new to this...

can anyone help me please can anyone solve this problem for me please Q) The Binomial distribution allows the calculation of the probability of k successes in n trails where there are only two outcomes: success or fail with probabilities p and q respectively. The Binomial probability is...

Homework Statement This is just a problem i came up with while doing in equations, and recently saw in a book too. Find the smallest integer n, for which n! > 10n The Attempt at a Solution The trial method (with help from the computer) yields 25 to be the answer. After a...

Got some exciting news from a PF Mentor: And the actual paper: http://iopscience.iop.org/1367-2630/12/12/123007 Violation of Leggett inequalities in orbital angular momentum subspaces J Romero, J Leach, B Jack, S M Barnett, M J Padgett and S Franke-Arnold J Romero et al 2010 New J...