# Search results

1. ### Is impulse an approximation?

Hi all, I am reading a book on spacecraft engineering in the section about trajectory dynamics. They define linear and angular momentum as: $I = \int_{0}^{\tau}{F}dt$ (Linear Momentum) $L = \int_{0}^{\tau}{T}dt$ (Angular Momentum) But they (and so many other sources) always mention the...
2. ### Root Locus Asymptotes

When sketching a root locus of a simple closed loop negative feedback system (with positive gain K).... if you have more poles than zeros, we know that they will tend towards infinity along some asymptotes. How do you know which pole will travel along which asymptote? For example in the...
3. ### Derivative of a Convolution

Hi, I want to verify that the form of a particular solution satisfies the following ODE: v' + (b/m)v = u/m with vpart= ∫e-(b/m)(t-r) (u(r)/m) dr where the limits are from 0 to t So I tried to differentiate v with respect to t, in order to substitute it back into the equation. But, how do...
4. ### Taking moments about a point

Conceptually, what does it actually mean to take the 'moments about a point' on a body, even if that point is not the center of rotation of the body (center of mass say). For example, we could take the moments about a point not even 'in' the body, so what does this value represent? I am...
5. ### Quick spherical coordinate question

So I have the following shape for which I want to calculate the inertia matrix. Basically I just want to know what limits of integration I should use if I am using spherical coordinates. Assume the convention that phi is the angle from x to y in the xy plane and theta is from z to the xy plane...
6. ### Systems of ODE: Converting complex solution to real

1. Homework Statement So, I have found a general solution to a system of linear first order ODE's and this is what I got: X = c1v1e^(-1+2i)t + c2v2e^(-1-2i)t where v1 = [-1+2i, 5], v2=[-1-2i,5]. The question is, how do I now change this solution into its real equivalent? i.e. I dont want any...
7. ### Entropy of an ideal gas

1. Homework Statement A liter of air, initially at room temperature and atmospheric pressure, is heated at constant pressure until it doubles in volume. Calculate the increase in its entropy during this process. Is there a way to calculate this using the thermodynamic identity (ie. without...
8. ### Scattering by a potential

"Scattering" by a potential When we have an unbound particle travelling past a potential well, what does it mean when it is said that the potential well will "scatter" the particle?
9. ### Phase-Space (density?)

So I think I have the basic idea of what phase-space is... basically a way of representing all possible states of a system in some n dimensional space. So, what then, is phase-space density?
10. ### Bosons and quantum states

I am doing some research on Bose-Einstein condensates and was hoping someone could give me a non-mathematical reason as to why bosons 'want' to occupy the same ground state. I think its details come from Bose-statistics, but is there a simplified way of explaining it? Thanks
11. ### Representing a wavefunction using bases

Can someone please explain why the representation of a wavefunction as an expansion of basis eigenfunctions actually gives us something of physical meaning? For example, it can tell us the probabilities of measuring a particular eigenvalue (depending on the expansion coefficients).... I mean its...
12. ### Differentiating complex numbers?

I am not sure whether there is any difference between differentiating complex and real numbers... I am just trying to differentiate: e^(2+3i)x = (2+3i)e^(2+3i)x Is this correct? I have a feeling its not this simple.
13. ### Parametric equations and derivatives

Just a quick question... if we have f(x,y,z) and x(t), y(t), z(t), without substituting in what x y and z are in f, how do we calculate df/dt?
14. ### Potential Wells

So I have looked up some related posts about potential wells but none of them really actually talk about what a potential well IS... what does the line on the graph actually tell us? what potential is it talking about?
15. ### Zero curvature => straight line proof

How would you prove that if the curvature of a 'curve' in R3 is zero that the line is straight? All I have learnt about is the Serret Frenet equations which I thought only apply when the curvature is non-zero? How do you define normals/binormals in this case? I'm not sure if this is enough...
16. ### Continuity of partial derivatives

What exactly does it mean for a function to have continuous partial derivatives? How do we see this?
17. ### Simulations - Programming languages?

I was wondering whether anyone has experience in astronomy simulations. If so, what language do you use and recommend? I've done Haskell and a very small bit of C++... I've been told Python is good, what are your thoughts? Also are there any good websites that may get me started? Thanks
18. ### Voltage across a solenoid

We are currently learning about solenoids in my physics class, and am very confused about where this potential drop comes from across a solenoid. I understand that an opposing electric field is created when a switch is first opened because of Faradays Law and the fact that the magnetic flux...
19. ### Induction for polynomial/sequence proof

1. Homework Statement Let k be a natural number, and r a real number with |r|<1. Prove (by induction on k) that for any polynomial P of degree k, there is a polynomial Q of degree k with Q(n+1)r^(n+1) - Q(n)r^n = P(n)r^n Hint: consider differences of successive terms for (n^k)(r^n) and use the...
20. ### What symbol?

My lecturer used a symbol in class that represents an element being removed from a set to form a new set. Does anyone know what this symbol is?
21. ### Making sure events are simultaneous in S'

I have a problem where it requires me to find when a laser should be fired at an asteroid to ensure that in the reference frame of the asteroid, the laser hits the back and front within 1 millisecond. I thought that I could define events in S' such that the front and back are hit at t' = 0, and...
22. ### Minimizing a vector in a triangle

1. Homework Statement A truck is to be towed using two ropes. If the resultant force is to be 950N, directed along the positive x axis, determine the magnitudes of forces F1 and F2 acting on each rope and the angle at which rope two pulls to ensure that the magnitude of F2 is a minimum. F1...
23. ### Continuous partial derivative?

My textbook describes how some functions are not well approximated by tangent planes at a particular point. For example f(x)= xy / (x^2 + y^2) for x /= 0 0 for x = 0 at (0,0) the partial derivatives exist and are zero but they are not continuous at...
24. ### Easy integral what am i doing wrong?

1. Homework Statement Integral[ x - 2|x|]dx from [-1,2] 3. The Attempt at a Solution Wouldn't it become x^2/2 - 2x^2/2 so x^2/2 - x^2 and then -x^2/2? So from [-1,2] it would just be -((2^2)/2) - - ((-1)^2/2) which is -1.5 but the answer is -3.5.....
25. ### Double integral under a cone

1. Homework Statement Use polar coordinates to find the volume of the given solid: Under the cone z = Sqrt[x^2 + y^2] Above the disk x^2 + y^2 <= 4 2. The attempt at a solution I tried using formatting but I couldnt get it right so I'll explain...I changed variables by making the upper and...
26. ### Angles in polar coordinates

I'm doing work on polar coordinates in double integrals. Could someone explain why when circles aren't centered on the origin the angle only varies from (if it is translated above the origin) 0 to pi. I thought the angle was supposed to be the angle in the circle, so if its a full circle then 0...
27. ### Double integral over circle region

1. Homework Statement So I have to use the type I type II region formula to find the volume under the equation (2x-y) and over the circular domain with center (0,0) and radius 2. Do I have to split this circle into semi-circles and treat it as 2 type I domains? I got the following limits for...
28. ### Double Integral over circle

So I have to use the type I type II region formula to find the volume under the equation (2x-y) and over the circular domain with center (0,0) and radius 2. Do I have to split this circle into hemispheres and treat it as 2 type I domains? I got the following limits for the top half, but I get...
29. ### Trig identity in complex multiplication

Just wondering how this is simplified to the third line: If w, z are complex numbers wz = rs( cos\alpha + isin \alpha ) (cos \varphi + isin \varphi) wz = rs(cos\alpha cos \varphi - sin \alphasin\varphi) + i(sin \alphacos\varphi + cos \alpha sin \varphi)) wz = rs(cos (\alpha...
30. ### Force on a polarized molecule due to a charged wire

1. Homework Statement A polarized water molecule is near a long charged wire and experiences a force due to the charge. How do you determine the net force on this molecule assuming the molecule is perpendicular to the center of the rod and nothing polarizes further. 3. The Attempt at a...