Diff eq Definition and 264 Threads

I have computed that the acceleration in my problem is a(t) = -gj - k/m(|r(t)| - L_0) * r(t)/|r(t)| Where a(t) is the acceleration vector, g is the gravitational acceleration, j is the unit vector in y-direction, k is the spring constant, m is the mass, r(t) is the position vector, |r(t)| is...

So I've derived the rocket equation in empty space and with constant gravity. Now I am interested in adding air resistance. I'm aware that there are 2 different models as if 0<Re<1 then F_drag=k*v and if 1000<Re<30000 then F_drag=1/2*A*rho*CD*v^2. And for my purpose the second model is most...

In order to obtain equation (3), I think I have to do the Fourier transform in the x direction: \begin{equation} \tilde{G}(k,y,x_0,y_0) = \int_{- \infty}^{\infty} G(x,y,x_0,y_0) e^{-i k x} dx \end{equation} So I have: \begin{equation} -k ^2 \tilde{G}(k,y,x_0,y_0) + \frac{\partial^2...

I have been going through my old books again, and found myself a little stuck. I am not entirely sure if this would be better in this one or diffy eq. The problem starts with having you find equation of motions when a= -bv, where b is constant and v = v(t) Using method of separable equations...

Homework Statement The evolution of the density in a system of attractive spheres can be described by the following dynamic equation. $$\frac{\partial}{\partial t} \rho (r,t) = D_o [\nabla^2 \rho (r,t) + \beta \nabla \rho (r,t) \int dr' [\nabla V (|r-r'|)] \rho (r',t) g(r,r',t)]$$ a)...

Homework Statement Hi I am looking at this derivation of differential equation satisfied by ##\phi(z)##. To start with, I know that such a disc ##D## described in the derivation can always be found because earlier in the lecture notes we proved that their exists an ##inf=min \omega ## for...

Homework Statement I have to calculate the critical points of the following system. $$x'=cx+10x^2$$ $$y'=x-2y$$ The Attempt at a Solution So I solve the system $$cx+10x^2=0$$ $$x-2y=0$$ So if $$x=2y$$ I have $$2yc+10*4y^2=2yc+40y^2=y(2c+40y)=0$$ and I get $$y=0$$ and $$y=-\frac{c}{20}$$ f I...

By using the laplace transform: $f(t)=sin(Φ(t))$ I want it in the form: F(S)/Φ(S) The purpose is to linearize it in order to put it into a larger transfer function, so far my only solution is to simplify it using taylor expansion.

I'm working on a personal math project and I'm running into this system of differential equations. I have seen references which state the solutions are in terms of Hermite modular elliptic functions, but I do not know what those functions are. All of the references I can find on this equation...

So I'm ordering some supplemental books to guide my education. I'm having a difficult time with physics and diff EQ this semester and am generally unhappy with how things are going in these classes. I'm looking for a few suggestions. I saw on another post that the following book is very good for...

We are studying 2nd and 3rd order differential equations in class, and have touched on superposition and were talking about an equation being linearly dependent or independent. I received some good explanations from tutors about this, using vectors as examples, but I'm still a bit unclear on the...

Homework Statement Find the general solution of the second order DE. y'' + 9y = 0 Homework EquationsThe Attempt at a Solution Problem is straight forward I just don't get why my answer is different than the books. So you get m^2 + 9 = 0 m = 3i and m = -3i so the general solution...

Homework Statement In problems 11-14 verify that the indicated function is an explicit solution of the given differential equation. Assume an appropriate interval I of definition for each solution. Question 13: y'' + y = tanx ; y = -cos(x)ln(sec(x) + tan(x)) Anyways, next problem... In...

Homework Statement L-1{[(2s-1)]/[(s^2)(s+1)^3]} Homework Equations L{f(t)e^(at)}=F(s-a) The Attempt at a Solution I have tried million ways but the different exponents in the denominator are throwing me off. The other problem is that I cannot use partial fractions, the homework instructions...

Hello Physics Forums! I'm in a little bit of an interesting situation. I've completed the classes offered at my school, but have been told that if I can directed-study these four courses they will provide me with a credit bearing exam for college undergraduate credit. Do you have any...

I have a question regarding a problem in chemistry. I ultimately solved it, but I wanted to know if the problem itself could be represented as a differential equation, and if the solution I found is the solution to that equation. The explanation is a little long, but I don't think I can make it...

Imagine I have a complicated second-order differential equation that I strongly suspect can be derived from a Hamiltonian (with additional momentum dependence beyond p2/2m, so the momentum is not simply mv, but I don't know what it is). Are there any ways to test whether or not the given...

Homework Statement For each of the following, determine if the system is linear. If not, clearly state why not. (a) ##y''(t)+15y'(t)+sin(y(t)))=u(t)## (b) ##y''(t)-y'(t)+3y(t)=u'(t)+u(t)## (c) ##y'(t)=u(t)## and ##z'(t)=u(t)-z(t)-y(t)## Homework Equations None The Attempt at a Solution...

Hello everyone. I'm an undergrad physics major with one semester left and I'm having some trouble. I took off 3 years to work on my depression and came back last spring to finish my senior year. Now, before I left I was struggling in all my classes due to my depression, but one was worse...

Hello guys, first I am sorry I didn't use the template. I deleted it by mistake and I didn't know how to create a new thread from scratch. so I have two cases of the same problem, on with initial conditions of pulling down and the other pushing up, I tried different signs but It didn't work...

Homework Statement Homework Equations The Attempt at a Solution this is my attempt, I figured this would be easier than typing. any how, I find partial fraction method is so time consuming and very algebraically complicated, is there a trick or another method I could use to make this...

Homework Statement Why do we need two solutions to solve a 2nd order linear differential equation? lets consider a differential equation with equal roots for auxiliary equation. So the reasoning behind why can't we use y=Aen1x+Ben2x as its general solution is because since the roots are equal...

Question : General solution of dy/dt = -ay + b My solution : dy/dt = -a(y-b/a) (dy/dt)/(y-(b/a)) = -a Integrating both sides : ln | y-(b/a) | = -at + C e(-at+C) = y-(b/a) Ce(-at) = y-(b/a)

Are there any known analytical method to solve the equation $$ A\frac{d^2f(x)}{dx^2}+B\frac{df(x)}{dx}+Ce^{igx}f(x) = 0\hspace{1cm}? $$ All quantities appearing in that equation are complex except for ##g## and ##x##.

Hey guys, so my professor told me to take a look at an equation, because he thinks that there is a mistake. We are basically talking about exercise 6.3 (on last image). The pictures will show you the text, so that you have all the information, that I have http://puu.sh/mrNDl/ec19cdff63.png...

Just a question about the theory of solutions to differential equations? Given a second order differential equation and two particular solutions y1 and y2, what is the best way to find the general solution? i.e variation of parameters or something else

I thought I understood how to solve these sorts of equations, but apparently not.. 1. Homework Statement In Linear Algebra I'm solving diff eqs with eigenvectors to get all the combinations that will solve for a diff eq. The text then asked me to check my answer by going back and solving...

Greetings all, I am registering for spring 2016 courses and have one question. I can pick up a math course and I have the option between two courses: 430 Formal Logic vs. 481 Applied Partial Differential Equations. I am a math and physics double major. Course list and description...

Homework Statement The mass of a car that acts on one wheel is 100 kg. The elasticity (spring) constant in the suspension system of that wheel is k = 10^4N/m. Design the strut (find the friction/resistance constant c) such that any vertical motion of the wheel (set up for example by going over...

Homework Statement Find the general solution to the equation. Homework Equations (dy/dx) - y - e^3x=0 The Attempt at a Solution [/B] I rewrote this as dy/dx - y = e^3x This is a linear first order ODE, in the form dy/dx + P(x)y = f(x) P(x) = 1; f(x) = e^3x The integrating factor =...

Homework Statement [/B] Hello all, I am looking more for an idea than an actual problem to solve. (That comes later.) Homework Equations I am starting a Differential Equations class, and I am looking for an idea for a project. We are to complete an application assignment in which we have to...

I'm trying to build a circuit to solve the differential equation x''+2x'+x = f(t), where f(t) is a sine wave with frequency 5Hz and amplitude 0.5V. I am supposed to get a sine/cosine wave (as the diff. eq is just the same as the ove governing spring-mass forced oscillation) as solution, but...

Homework Statement Find the specific solution for: y''-2y'+y=xe^x+4, y(0)=1, y'(0)=1. Homework Equations N/A The Attempt at a Solution Since xe^x is already in the general solution of the homogeneous version of this diff eq (complementary solution), my first guess for a partial solution...

Homework Statement Consider the first-order non-autonomous equation ##x' = p(t) x##, where ##p(t) ## is differentiable and periodic with period ##T##. Prove that all solutions of this equation are period with period ##T## if and only if ##\int_0^T p(s) ds = 0##. Homework EquationsThe Attempt...

[b] Homework Equations N/a The Attempt at a Solution I am wondering if this is the right direction in solving this. any input would be great! Sorry for the messy handwriting!

Hi. First off, sorry for the not so descriptive title. If one of you finds a better tilte I will edit it. We have the equation \begin{equation} \partial_{xx}\phi = -\phi + \phi^{3} + \epsilon \left(1- \phi^{2}\right) \end{equation} We will look for solutions satisfying...

I was thinking about some form of classify all kinds of equations and system of equations. And the better classification that I found is by 1st to classify if the equation represents a curve or a surface. Represents a curve if the spatial coordinates are functions of an unique variable and...

Hi everyone, this is my first post and so I just want to say thank you in advance for any responses to my question. I recently applied for an internship which will take place over the summer of 2014 and it looks like I have a good chance at actually being accepted for the program. However, I...

Good morning everyone. I need some guidance regarding which course to take next semester. For some background, I am active duty Navy with three kids majoring in Mechanical Engineering. Due to my work schedule, I can only take 2 classes per semester (for now). I am already locked into Physics...

Homework Statement From Boyce and DiPrima's Elementary Differential Equations (9th Ed.), Section 6.5, Problem 13: Consider again the system in Example 1: 2y'' + y' + 2y = \delta(t-5); y(0)=y'(0)=0 (Solution in text...

Homework Statement determine whether the given differential equations are homogenous and, if so, solve them. Homework Equations dy/dx = (( x^2 -2y^2)/xy ) The Attempt at a Solution i assumed it was homoG. Then i replaced ( x*v) for each Y and made dy/dx --> v+x*(dv/dx)...

Homework Statement For the following differential equation: dy/dx = \frac{2cos^2x-sin^2x+y^2}{2 cosx} , -pi/2 < x < pi/2 show that the substitution y(x)=sin x + 1/u(x) yeilds the differential equation for u(x), du/dx = -u tan x - \frac{1}{2}sec x Hence find the solution y(x) to...

Homework Statement \frac{dx}{dt}=x-x^{2}Homework Equations The Attempt at a Solution I think the only thing I have wrong so far is how to finish it because I can't find anything wrong with my work, but I don't know how the book gets their final answer. Separate variables... \int...

Graphing diff eq slope field with TI Nspire CX CAS HELP please!? Every time I try to graph a slope field an error message pops up saying 'wrong number of initial conditions'. What does this mean? I tried graphing equations like dy/dt = t^(2) + t or dy/dt = 1-2y but I keep getting that dumb...

Homework Statement Find the value of k for which the constant function x(t)=k is a solution of the differential equation 6t^5dx/dt+7x−4=0. The Attempt at a Solution I have tried this several ways but no luck, here is one of my attempts, solve for dx/dt, dx/dt = (4-7x)/6t^5 take the...

Homework Statement Determine the general solution of: y(6) + y''' = t The Attempt at a Solution Ok, r = 0, 0, 0, 1/2 +- 3i/√2, -1/2 + 3i/√2 What do I do with that last r value? It turns into ce-t somehow, but I don't see it. edit: typed a number in wrong, fixed now~

Homework Statement Hello, maybe this is due to my lack of understand of RK4, but I have an equation: x'' + b^2*x=0 (derivatives with respect to variable t) and I need to use RK4 to find the solution on an interval. I can readily find solutions analytically, but my understanding of RK4...

Homework Statement Suppose a water tower in an earthquake acts as a mass-spring system. Assume that the container on top is full and the water does not move around. The container then acts as a mass and the support acts as the spring, where the induced vibrations are horizontal. Suppose that...

Homework Statement Show that y1(t) and y2(t) are solutions to a certain differential equation. Homework Equations The Attempt at a Solution I plug both of these into my diff. eq. and I got the same thing. How is this showing that they are solutions to a diff. eq.? What if I got a different...

Homework Statement (1) Suppose you have a spring with spring constant 4 N/m. You want to use it to weigh items. Assume no friction. You place the mass on the spring and put it in motion. a) You count and find that the frequency is 0.8 Hz (cycles per second). What is the mass? b) Find a...