Hard Definition and 1000 Threads

Homework Statement A 0.750kg block of wood is attatched to a spring with k = 300N/m. A 0.0030kg bullet is fired into the block, and the spring is compressed 0.102m. Calculate the velocity of the bullet before the collision. Is this elastic or inelastic? Homework Equations How do you do...

This question was posted in the homework forum. To my understanding, this looks like two different questions as the first hypothesis is not true due to a simple counter-example argument. The second one would be true by two induction arguments on k>2 and k<0. Am I wrong in thinking this? It...

Homework Statement Find the polynomal that approximates the integral of (t^2)e^-t^2 from 0 to x, [0,1], with an error less than 10^-3 Homework Equations You need to use taylor theorem & remainder estimation theorem The Attempt at a Solution I set up the tailor series with the first 4 terms...

Prove that if ##m > 1## such that there exists a ##c > 1## that satisfies $$cm < m^c$$ then for any ##k > c## $$km < m^k$$ holds. Prove this without using logarithms or exponents or calculus. Basically using the properties of real numbers to prove this. One attempt I have tried, but didn't...

Homework Statement At very low temperatures, the molar specific heat of many substances varies as the cube of the absolute temperature: C=k*(T^3/To^3), which is sometimes called Debye's law. For rock salt, To= 281K and k= 1940 J/mol*K Determine the heat needed to raise 2.40 mol of salt from...

Hello everybody! I'm now in the second half of my PhD program, with 2 more years to go, and nothing to show for it. Sure, I've written two papers (which got zero citations), but the only good thing I can say about these papers, is that they are not the worst papers ever written...

Homework Statement integrate the following function: x*√(2x-x2) Homework Equations substitutions? The Attempt at a Solution I substituted x with x=2sin2u. From that I ended up with ∫x*√(2x-x2)= 16∫sin4u*cos2u Now I'm supposed to use a formula from an integrals table.. but which?

I'm considering taking mechanics (lagrange/hamilton etc.) my second year coming out of physics II (electromagnetism), but I've heard it's a very difficult course. In fact my advisor advised against me taking it since i have the prerequesites but not the "experience". The problem is the usual...

Homework Statement Taking k and ω to be constant, ∂z/∂θ and ∂z/∂ф in terms of x and t for the following function z = cos(kx-ωt), where θ=t2-x and ф = x2+t. Homework Equations The Attempt at a Solution I'm finding this difficult as t and x are not stated explicitly. I know how to...

I am looking at questions like 1/(x+4)>x-4 or 1/(x+7)>x-7 I have no idea how to solve them, I have simplified to (-x^2+50) /(7+x) however I don't think it is correct and I don't know what do do from there.

1. Homework Statement An airplane begins its takeoff sequence moving with a constant acceleration a. A passenger holds up a pocketwatch during the takeoff sequence and notices that the watch makes an angle θ = 14° with the vertical, and that 13.3 seconds pass before the plane leaves the runway...

If I have a body (for simplicity a cube with side d) on a fluid (with density ρ) with its top at a depth h, the force acting on top of it is ma = (h*d*d)*ρ*(g); where g is the acceleration of gravity, (d*d*h) is the volume of the column of liquid on top of the cube and that times ρ is the mass...

So, I was tutoring a friend in math, and he was working in pencil and I noticed that he presses really hard into the paper. In fact, the tip of his pencil broke and I had to loan him my mechanical pencil. That was pretty disastrous because the thin lead snapped every few seconds. He went through...

Homework Statement An airplane begins its takeoff sequence moving with a constant acceleration a. A passenger holds up a pocketwatch during the takeoff sequence and notices that the watch makes an angle θ = 14° with the vertical, and that 13.3 seconds pass before the plane leaves the runway...

I have a very hard time cleaning out the hard water stain and soap scum on the shower door glass. I tried the normal cleaning spray. I tried using Vinegar( acetic acid), Lime juice (citric acid) with no luck at all. Any suggestion on what I can try?

Please intergrate: (x+3)/(x^2+4x) is it even possible to integrate this? The question in the book was (x+2)/(x^2+4x) and it can nicely be integrated to 0.5ln(x^2+4x), but by changing the 2 to a 3 f'(x) don't go into each other. if you know what i mean.

Homework Statement The Gravitron single-car roller coaster consists of a single loop-the-loop. The car is initially pushed, giving it just the right mechanical energy so the riders on the coaster will feel "weightless" when they pass through the top of the circular arc. How heavy will they...

A properly prepared and painted piece of steel can go for decades without the slightest bit of rust. If however you start with a piece that has started to rust and paint over the rust, it does not last more then a year or two at best before the rust is causing damage again. Why is this? The...

$$\frac{d}{dx} \frac{x}{\sqrt{x^2+3}}$$ I've been trying to get this for an hour now and I just get a mess; could anyone lend me a hand to see where I'm going wrong? thx, DeusAbs

In a COB product with FR-4 substrate, blue light chip excites yellow phosphor to form white light. Why is room temperature aging attenuation higher than 85 degree/85% RH aging attenuation? (After 1000h lighting, Attr=7% while Att85=1%) (If you have further questions about how I do the...

I don't know if this is the right forum. Please move it to a better suited one if it exists. Basic info: I am a sophomore taking Modern Physics and will be having my first exam this thursday. I've solved a healthy amount of problems already, but I wouldn't mind being as prepared as possible...

I just did a clean install of Windows 7 64 bit on my system. unfortunately I misplaced the box of CDs with most of my applications. I still have the hard drive where all the apps are installed. is it possible to extract the entire application from the old HD and install it on the new one? I have...

Well, I found this challenge in another forum (not about math) on the internet, and, originally, there were no 'w', 'z' or 'y' drawn on the pic, it was just "find the x", but I put them on because I know you guys probably would create other variables to solve the problem. Another problem I had...

I just got my 1st textbook today, University Physics with Modern Physics. MY GOD. THE THING IS HUGE:eek: It's 1600 pages. And the pages are wafer thin as well which kinda sucks... I think they might rip a bit too easily. But it makes me think, I have to cover the entire book in one year...

Hello, I am currently signed up for Fall Quarter Engineering Physics, Diff EQ, and Matrix algebra at the University of Washington. Right now I am sort of skeptical if I should drop one of these classes because I have heard horror stories from at least one of each of these classes. I got a B-...

What textbook do experts here recommend for a first course in DC/AC circuit analysis? I've checked what many universities use in EE, and reviewed some of these texts. However I see they almost have the same outline of topics but they differ slightly in how they approach each topic. Some...

Why are ionic compounds hard and brittle ? For instance, an alloy is a mixture of 2 or more elements and thus does not break easily relative to original elements. Shouldn't the ionic compounds also be like the alloys ?

The wikipedia article on collisions says "collisions between hard spheres may be nearly elastic". It doesn't elaborate nor give a source on the statement. I was wondering about those two conditions. Hardness I understand, but is the spherical shape necessary? Is it about there being a single...

Homework Statement Simplify the following: sin(b)/cos(b) + cos(b)/sin(b) Homework Equations Trigonometric identities The Attempt at a Solution Ok so i have no clue how to do this,I keep trying but can't seem to get the right answer, I have tried to do this: sin(b)/cos(b) +...

My portable hard drive has died on me, is there any software (preferably free) that can help recover the contents?

This problem is*using*real*data*of*the*first*extrasolar*planet*discovered*around *a normal*star*to*calculate*the mass of the planet. I am really stumped on this equation.I put it as an attachment because I had a hard time entering it by keyboard. So far I figured out from graphs and conversions...

I have this problem and I need help .. please School problem, it has been my second semester in college and I am doing really bad. I know I am not studying as much as I should. But every time I open the book , I start thinking of something else …. Seriously I tried all my best to concentrate...

My Calc III teacher this fall gives take home exams because he insists that there isn't enough time to cover all the material in Calc III, so he needs every class hour to teach, thus he gives take-home tests. Knowing people who took his calc III class last fall, and him curving an A to be 70%, I...

Homework Statement Integral, from 0 to 1, y/(e^2y) Homework Equations Use integration by partsThe Attempt at a Solution I need integration by parts. The answer is 1/4-3/5e^-2. But I got 1/2 and it all makes sense to me, so tell me what I got wrong. I put u=e^2y du=2e^2y dv= 1/e^2y dy (did...

Homework Statement Integral, from 4 to 6, 1/(t^2-9) dt Homework Equations please use my approach to solve it, like with cosh and whatnot The Attempt at a Solution Integral, from 4 to 6, 1/(t^2-9) dt so I multiplied the top and bottom by square root of 9. which got me...

i was reading an article about the Kaman K-max being used as a UAV, and there were comments about how this helicopter is harder to fly than a traditional main-and-tail-rotor helicopter ... the large number of accidents of the K-max also seems to suggest the same thing why is this? to me, the...

Hullo chaps. Sorry to bother you with this, but I need some help. Is it possible to, having taken up to Algebra II (yes I'm underage, yes it's pathetic), quickly review everything you learned during the High School Algebra courses and then use a Calculus text like Apostol I to review what is...

Homework Statement Find the derivative of sin(tan(square root of sinx)) Homework Equations derivative of: sin=cos tan=sec squared sinx=cosx The Attempt at a Solution cos(tan(square root of sinx))(sin(sec^2(1/2sinx)^-1/2(cosx)) So I did the derivative of the sin, left...

Homework Statement A string is attached to the drum (radius r) of a spool (radius R). (A spool is device for storing string, thread etc.) A tension T is applied to the string at angle θ above the horizontal. The coefficients of kinetic and static friction between floor and spool are μk and...

I recently performed an XRF spectroscopy on a metal foil in a materials lab for school and I;m having trouble reasoning out an answer, though it's probably an easy one. The idea behind the lab is, we are given a bi-metal foil, which is either an alloy or a "sandwich" of two thin sheets of metal...

[SOLVED] A hard differential equation - where is the error in my logic? Homework Statement 2xyy' + y2, where y is a function of x The Attempt at a Solution 2xyy' + y2 = 12x2 |*(1/x) => (y2)' + y2/x =12x |*ln(x), 2yy' = (y2)' => (y2ln(x))' = 12x*ln(x) => y2ln(x) = ∫12x*ln(x) =>...

Homework Statement What is the next number in the following series? 1 2 12 48 216 936 4104 17928 78408 342792 ____________ Homework Equations I haven't any ideaThe Attempt at a Solution power's of two, powers of three, prime numbers. I am beat it can be found on this test...

Homework Statement The hard drives of many desktop computers spin at a maximum rate of 7200 rpm. If the diameter of the spinning disk in the harddrive is 3.51 cm, calculate the magnitude of the centripetal acceleration on the outside radius of the disk. Homework Equations ac=v2/r...

Before the days of fast internet access, I eagerly made copies of interesting technical articles. I even bound them up using "stab binding". However, the way they piled up was a depressing reminder of all the knowledge that I was never going to take time to investigate. Now that the internet...

in terms of what buying what is the dereference between hard and soft iron? i know an iron core is good but what about cast iron?

Homework Statement I have attached the question Homework Equations The Attempt at a Solution so the first thing I did was find the frequency = 120 Hz The next thing I did was find the circumference = 0.2796 m (from pi*d) Now I know that the answer is no. magnets per disk *...

Homework Statement A very light rigid rod with a length of 0.062 m extends straight out from one end of a metre stick. The combination is suspended from a pivot at the upper end of the rod as shown in the following figure. The combination is then pulled out by a small angle and released...

Homework Statement For this problem assume that the 365 dates of the year are equally likely as birthdays. b)Find the probability that in a group of n people, at least two have the same birthday. Homework Equations The Attempt at a Solution Well I am not really sure what...

My question is pretty much what i wrote in the title, I'm wondering how hard a phd in mathematics from mit or an ivy league univ would be.

Tuberculosis pathology is hard! Hello, I'm reading tuberculosis pathology and I'm finding it hard to understand because my general poor knowledge in pathology. This is what I gathered from the reading. 1. Tubercle bacilli reach alveoli of lung and ingested by macrophages. 2. Then...