# Search results

1. ### Engineering To quit or not to quit

Hello PF again! I'm really what I think in a very difficult situation. I've got an undergrad degree in Aeronautical/Aerospace Engineering, and I'm now doing my masters in the same field and working a job that pays really well and my prof asked me to join one of his projects. There are I think...
2. ### Feasible Directions & FONC

1. Homework Statement \text{Minimize } f(x) \text{Subject to } \Omega where f:R^2 → R \text{ is given by } f(x) = -3x_1 \text{ where } x = [2,0]^\top \text{ and } \Omega = \{x: x_1 + 2x_2^2 \leq 2\} \text{Does the point } x^* = [2,0]^\top \text{satisfy F.O.N.C?} 2. Homework...
3. ### Richard Feynman - Proportion

Hi everyone. I don't know if this is the right place for this thread, but I couldn't find a better one. In one of the Feynman's interviews, he says "So …altogether I can’t believe the special stories that’ve been made up about our relationship to the universe at large because they seem to...
4. ### Probability to Find a Particle

1. Homework Statement Suppose we have a particle in 1-dimension, with wavefunction Ae^{-\frac{|x|}{2d}} . What is the probability to find the particle in the interval [0,d]? Please provide your answer in terms of A, d, mathematical constants such as π (entered as pi) or e (entered as e)...
5. ### Taylor Approximation

1. Homework Statement Show that ∫f'(x)dx/f(x) = ln|(f(x)|+C where f(x) is a differential function. 2. Homework Equations First order Taylor approximation? f(x)=f(a)+f'(a)(x-a) 3. The Attempt at a Solution Well, I'm not really sure how to approach the question. It's my...
6. ### Must we have black holes?

As the title says, do we have to have black holes for the universe to run? Every galaxy has a suppermasive black hole at its center. What if there were a star at the center of our galaxy? I guess it would have to be so big but that means the star would soon run out of energy and then explode...
7. ### Magnetlike particle and Light

Hi. When we turn on a lamp in the room at night, the room gets bright. Now, is there such a thing that does the same thing but other way around? When, it's not night, i.e day, we turn the lamp on and it absorbs all the light in the room and make the room dark? I guess such a lamp would be...
8. ### Speed of Swallow of a Black Hole

Hello everyone. As far as I know, even lights can not escape from black hole once the light reaches to even horizon as lights carry momentum hence energy. Now, what I wonder is, how fast do black holes swallow light or, if you will, other objects? I guess it cannot be faster than the speed of...
9. ### Rod/Stick's Velocity

1. Homework Statement http://i.imgur.com/toGAIGP.png?1 BC is vertical at the given position Calculate the velocity and acceleration of the point C. 2. Homework Equations V = Ï‰*r 3. The Attempt at a Solution I guess, AB, BC and CD rods have the same angular speed Ï‰ = 12 rad/s. And...
10. ### The Observable Universe ve The Universe

Hello everyone. As I was reading an article on wiki, I stumbled upon this by chance; If the universe is finite but unbounded, it is also possible that the universe is smaller than the observable universe. In this case, what we take to be very distant galaxies may actually be duplicate images of...
11. ### Frequency, Velocity and Wavelength of Light

Hello all. When light goes through one medium to another, its velocity and wavelength change but frequency remains the same. If the wavelength of light decreases, the length between two crests decreases, doesn't that mean there will be more wave hence frequency will have to increase? I tried to...
12. ### Invention of Alternating Current

Hello physicsforums. I'd like to apologize for submitting such a fool thread. Anyway, I'm in disagreemeent with my friend who thinks it was Nikola Tesla who invented AC, but I insist that it was not him. I tried to google it, but I have yet to find a proper answer. He's like, " My physics...
13. ### Heat Death

Hello. I a few hours ago opened a new thread called "Big Crunch". But now that I've learn that it's not really possible for Big Crunch to happen, I also look for another possibilities. It looks like the best theory is Heat Death. It says that all stars will be dead the temperature will be the...
14. ### Questions about Big Crunch

Questions about "Big Crunch" http://map.gsfc.nasa.gov/universe/uni_shape.html From the picture above, it looks like the universe has three kinds of shapes. ( Density>1, density<1, density=1) So how the density of the universe will be(if it'll ever) be smaller than 1? How does it change...
15. ### Dark Energy and Life?

Hi everyone. I wonder if life and dark energy have something in common or are related to each other. If our universe had more dark energy than it now has, e.g 90% of the universe was filled with dark energy, would we still be able to live? The more dark energy, the fewer the chances of us being...
16. ### Hypercube 4th Dimension

Hello everyone once again. If I remember correctly, hypercubes are said to have 4th dimension. But as far as I know, the 4th dimension is time. So, when we're describing the 4th dimension I guess we can say, " Let's meet at my house at 12.20 pm". When I say "at my house" I'm talking about the...
17. ### Subatomic Particles From Nothing?

Hello everyone. I once read an article saying subatomic particles can exist from nothing in a vacuumed space( or something like that). Is that even possible? Or does the energy vacuumed space has turn into mass/matter, hence we thing it exists from nothing?
18. ### Mass/Energy Creation and Conservation

Hello everyone. First of all, I should like to apologize if the question I'm going to ask looks so ridiculous. As far as I know, energy can't be destroyed or created. It only changes forms. So far so good, but how in the beggining did it occur? How was it created? Where/How did the first energy...
19. ### Cosmos like book/documentary/movie

Hello everyone. First of all, I'd like to apologize if this isn't the right place to open a new thread. I would like to buy a book or watch a film about the cosmos. I watched Cosmos by Carl Sagan it was really worth watching. However, since I'm going on a vocation in a month, I'd like to order a...
20. ### Rational Root Thorem

1. Homework Statement x4 - 4(x3) + 3(x2) -2x +1 = 0 2. Homework Equations Rational Root Theorem, q/p 3. The Attempt at a Solution Hello everyone. Today, I've learnt the rational root theorem( it's a bit late, isn't it? :( ) and thus wanted to see how it works. According to...
21. ### I think I'm lost about my future

Hello everyone. Before I start asking my question, I'd like to, if I may, talk about myself. I'm currently studying Aeronautical/Aerospace engineering and the following year will be my third year(including undergraduate preparotry). But, I don't really want to be an engineer, but a mathemetician...
22. ### Uniform Circular Motion

1. Homework Statement An object is in uniform circular motion. As the time passes by, its mass decreases. ( It has Co2 in it, and it evaporates) What will happen to the object's velocity and angular momentum? 2. Homework Equations F = mV²/r, L = mvr 3. The Attempt at a...
23. ### Comp Sci Fortran Matrix Multiplication

Hi. Write an external function that takes two matrices, multiplies them and returns the resulting matrix. Matrices can be of any dimension. Print the resulting matrix The above is what I have to do. http://paste.servut.us/pgmm This is what I've done so far. But it seems like...
24. ### Language and Programming Language Aero- Engineering

Hello everyone. I'm now currently studying Aeronautical Engineering(Though it's, I think, said to be equal to aerospace engineering). Since the summer is coming and I'll have like free 4 months, I've decided to learn another language(s) besides English and Fortran(Both the language we speak and...
25. ### Comp Sci Searching on Fortran

Write a program that creates a phone-book (Name, Surname, Phone Number). Ask the user the number of entries Read user input to an array Write this array into a file in the hard-disk Your program should avoid multiple entries! If a record already exists in the phone-book, the program should...
26. ### Fortran Fortran - Having to add integer command

Hello everyone. Today I learnt how to write a program which calculates and prints integer squares roots from 1 to 1000. Here is what I wrote: program example real::i do i=1,1000 if(sqrt(i)**2==i) then print*,i end if end do end program example After compling this, 25, 49 etcs can't...