Cross Definition and 1000 Threads

Homework Statement (u X v) X w = u X (v X w) Iff (u X w) X v = 0 Homework Equations (u X v) = -(v X u) The Attempt at a Solution I know that I am supposed to prove this by proving P --> Q and Q --> P I know that if (u X w) X V = 0 then (u X w) is a scalar multiple of v. How...

tex doesn't seem to be working right...sry for the notation. Working through of a proof of the generalized jordan curve theorem. Keep getting stuck on calculating the reduced homology of S^n by R, (ie n-sphere cross the real line). My book (hatcher) seems to imply its 0 except the n^th...

Hey, The hard cross-section of a 2 to 2 inelastic scattering goes as 1/E^2, where E is the center of mass energy. However, the cross-section in proton proton collisions increases with energy. My question is; does anybody have a good explanation for this and/or a good reference where I can...

Homework Statement Find the volume of a solid whose base bounded by y=x+1 and y=x^2-1, with cross section of a square perpendicular to x-axis The Attempt at a Solution So i set up the problem like this delta volume= y^2*delta x, that being the area of the square where i get loss is...

Homework Statement Let P be a point not on the plane that passes through the points Q, R and S. show that the distance d from P to the plane is d = (|a.(bxc)|)/(|axb|) where a = QR and b = QS and c = QP (those are lines between given two points) Homework Equations |axb| =...

This might be math problem, but I only see it in EM books. \nabla X (\vec A X \vec B) \;=\; (\vec B \cdot \nabla)\vec A - \vec B(\nabla \cdot \vec A) -(\vec A \cdot \nabla)\vec B + \vec A ( \nabla \cdot \vec B) . What is \vec A \cdot \nabla ?

Homework Statement Hi there. I am currently taking physics 30(algebra physics course) and we are in the electrostatics unit. I am curious as to why, when trying to find the force acting on a charged particle moving perpendicular to a magnetic field, the force results in a direction that is...

Gymnast pictured below performing an Iron Cross has a mass of 65.00 kg. Assume that the forces in the cables are symmetric and that he is in static equilibrium. A. Draw a complete free body diagram of the gymnast (just him – he is the system). B. Calculate the vertical and horizontal...

in a many particle system we have a center of mass R and position vector of the ith particle with respect to centre of mass is r_i. hence the position vector measured from the origin is R_i=R+r_i. why does R\times\sum (m_i \dot{r}_i) =0, where \dot{r}_i denotes the rate of change wrt time...

Homework Statement Two vectors A and B have magnitude A = 2.99 and B = 3.10. Their vector product is A X B = -4.98 k + 2.08 i . What is the angle between A and B? Homework Equations C= ABsinθ C=A X B The Attempt at a Solution θ= arcsin C/(⎮A⎮⎮B⎮) so i found the magnitude...

Hi, If a particle falls radially into a Reissner-Nordstrom BH with Q<M (i.e the case where you have an inner and and out horizon), then where in the conformal diagram does the test particle cross the inner horizon r_{-}? See for example the righthand Penrose diagram of...

Homework Statement I already made a start to this question, the position vectors below are worked out in the first part of it, I am 99% sure they are correct so, on to the bit I am stuck on. :) A player stands with his feet at the point O and serves the ball from a point Y at a height of...

I have a number of books which give a vector identity equation for the curl of a cross product thus: \nabla \times \left(a \times b \right) = a \left( \nabla \cdot b \right) + \left( b \cdot \nabla \right) a - b \left( \nabla \cdot a \right) - \left( a \cdot \nabla \right) b But doesn't b...

Homework Statement I do need to calculate the mean free path for an ion with a radius of 9 x 10‐8 cm in pressures of 10‐8 Torr, 10‐6 Torr, 10‐4 Torr and 10‐2 Torr Homework Equations There are different equations I found but the most one is λ= 1/Nσ N gas number density which I do not...

Does anyone knows how to compute cross product vector of more than 3 dimensions? It seems all the linear algebra textbooks only discuss 3D cross product vector. What are the formulas?

Homework Statement Calculate the differential cross section for A+B---> C+D with an invariant matrix element Homework Equations See attachment The Attempt at a Solution I have no idea how to even begin this problem. The course I am taking is an undergraduate course in intermediate modern...

I've been trying to find what the square of two cross products is and can't find it. Can anyone tell me the identity for (A X B)^2 ?

Homework Statement I have to do an E&M problem, I think I got it, but I made a few steps that I don't really understand. The first one is: If delxB= muJ Does del x dB/dt = mu dJ/dt ?? If so, why ? I tried using latex, but it didn't work...sorry :( Homework Equations...

Homework Statement A cmedium carbon steel rod has a rectangular cross section and must cope with a tension of 29 430 Newtons . The thickness of the rod is 15 mm calculate the siz of the cross section? Homework Equations A=P/Ok [b]3. The Attempt at a Solution [/b O = UTS = 750...

Assume that X^1,X^2,\ldots, X^k are vectors in \mathbb{R}^n, and 1\leq k\leq n. Is there a simple formula for the k-dimensional measure of the generalised "quadrangle" spanned by these vectors? If k=n, then the solution is |\textrm{det}(X)| with X_{ij}=(X^{j})_i. If k=2 and n=3, then the...

cross product question.. "find the magnitude of the force" Homework Statement A wrench 0.9 meters long lies along the positive y-axis, and grips a bolt at the origin. A force is applied in the direction of <0, 3, -2> at the end of the wrench. Find the magnitude of the force in Newtons...

Homework Statement If the cross product of vector v cross vector w = 3i + j + 4k, and the dot product of vector v dot vector w = 4, and theta is the angle between vector v and vector w, find tan(theta) and theta. Homework Equations vector c = |v||w| sin(theta) where vector c is the...

Homework Statement I have 2 (3d)vectors A and B and I want to find a vector C perpendicular to both of them. A = 3i-2j+4k B = -2i+5j-2k C = Cx+Cy+Cz Homework Equations So we know A dot C = 3Cx-2Cy+4Cz and B dot C = -2Cx+5Cy-2Cz The Attempt at a Solution

Homework Statement Find the distance from the point (2, 4, 4) to the line x = 0, y = 4 + 3t, z = 4 + 2t. Homework Equations The cross product and the dot product and d = |n * b|/|n| The Attempt at a Solution So the distance from the point to the line is the line directly...

Homework Statement show (axb) . (cxd) = |a.c b.c| |a.d b.d| The Attempt at a Solution i have no idea. i don't know if the lines at the side are modulus lines or matrix brackets but it seems that it has something to do with distribution law. but i can't start proving if i...

out of interest does cross sectional area change when a force is applied (lets say I had a wire and I applied a force to it, the wire would stretch ) does its cross sectional area change

The cross section for scattering by a Coulomb potential 1/r is the same for both classical and quantum mechanics, and the total cross section is infinite. I understand this classically as saying that no matter how large an impact parameter an incoming particle has, it will still be deflected at...

An orientation of a real n dimensional vector space V is an equivalence class of an ordered basis. Equivalently, this corresponds to a choice of a generator of H_n(V,V-0)=Z. The correspondence between the two is this: given an ordered basis (v_1,...,v_n) of V, the convex hull of...

Hi, I've been trying to derive the electromagnetic stress tensor on my own, and I've run into a bit of a problem. I have a cross product of a curl (\vec{E}\times(\nabla\times\vec{E})) that I need to expand, and the typical...

Hey guys, I'm a kinda noobie to this site so I have not much experience with the formatting and stuff here, but anyway was doing some physics and came stuck =P Would really appreciate any help Homework Statement Vectors A and B are drawn from a common point, with the angle in between them...

Homework Statement There are two points p1 pointing up p2 pointing rightHomework Equations The Attempt at a Solution I need to find \stackrel{\rightarrow}{p1} * r^ \stackrel{\rightarrow}{p2} X p1^ \stackrel{\rightarrow}{p2}* r^ they got \stackrel{->}{p1} * r^ =0 why is that? i know...

Homework Statement This is a physics problem. need to find torque on dipoles the the 2 dipoles are on the same plane with distance r p1 is pointing up while p2 is pointing right Homework Equations N=PxE The Attempt at a Solution I know how to do a cross product, you make the...

A 5.0 kg object at r= i^+2j^+3k^ meters has an acceleration a=5i^+6j^-7k^ m/s^2 a)what is the objects torque around the origin of the cordinate system b)prove that the torque is perpendicular to the position vector r a) t^=rXma=-10<16,-11,2> t=-10(381)^1/2 b) <1,2,3>*<16,-11,2>=0

Could someone please clarify a simple order of operations related to cross product? A x (B x C) = ? I am not sure between the these two options: = (A X B) x (A X C) or = do stuff in parenthesis first then cross with A

My final for Physics is coming up and I really, really ****ed up in this class. I don't even know how to do dot products, cross products, or let alone Newton's laws. We applied Newton's laws to some pulley problems I think. I've been going to all the lectures but it just doesn't stick -- nothing...

Can I use cyclic rotation in \vec{a} = \vec{b} x \vec{c} and say: \vec{c} = \vec{a} x \vec{b} \vec{b} = \vec{c} x \vec{a} for any vectors \vec{a}, \vec{b} and \vec{c} or only if they are perpendicular to each other? If it's only a special case: is there a way to express \vec{b} and...

hi how to calculate the traces of product of Dirac matrices in QED. i want caculate crossection of process scattering in QED. a program to calculate it

Does anyone know how SolidWorks calculates the stresses for this simulation. Can anyone give me an idea, is it second moment of area? y/r = m/i? Thanks Richard.

Homework Statement Show that \displaystyle\lim_{\underline{h}\to 0} \frac{\underline{c} \times \underline{h}}{\|\underline{h}\|} =0 where c and h are vectors and x denotes cross product. Homework Equations The Attempt at a Solution No idea how to do this?

Homework Statement cross product of i x -i Homework Equations i x i =0, i x j = k, etc. The Attempt at a Solution I'm guessing it would be zero, just making sure because I keep getting the question I'm working on wrong.

Hello there folks. So I'm doing some homework, and one of the questions asks for a comparison of the microscopic absorption cross sections of B, Cd, Gd, and Hf with the fission cross section of U-235. I've found the fission cross section in my trusty 17th edition of Nuclides and Isotopes, but...

I was ask to find the Cross Sectional Flow Area of a air duct given this question : The air duct is a vertically mounted duct of 65mm by 150mm cross-section and approx. 1.2m long. My working is like this: 65 x 150 = 9750mm2 I just wanted to clarify if my working is right. Another...

Homework Statement I'm solving a physics problem using cross products and I think I might be doing the cross products wrong Homework Equations I'm using the formula: a cross b = (a2b3- a3b2)x + (a3b1- a1b3)y + (a1b2- a2b1)z where a1 = ax, a2 = ay, a3 = az, etc. I don't know if this...

Photon interaction cross section? What?!? Hey guys-- I'm practicing for the GRE, and I came across a question that has stuff that's not even in my textbook! I haven't found much from googling either. Here is the question: My instinct was to guess (C) because graphs I had seen of the...

Hello! I have a quick question regarding the intersection of three planes if the determinant is 0. If there are solutions, there will be an infinite number of solutions. One of the equations for the plane can be ignored as it is a linear combination of the other two, and can be ignored for...

If Fmag = q(v x B) and Felectric = qE, Florentz = q [E + (v x B)] can I say that Florentz = Fmag + Felectric?

And goes directly through Oregon. Woohoo! http://eclipse.gsfc.nasa.gov/SEgoogle/SEgoogle2001/SE2017Aug21Tgoogle.html

Do you know people who work in both string and non string QGs, or who changed from string to non string or vice versa?

Homework Statement A rod has one end at the origin and one end at the point P whose coordinates are (1m, 2m, 2m). A force F = (3i+2j-1k) N acts on the rod at the point P. What is the torque about the origin due to F? Homework Equations torque = F x r The Attempt at a Solution I'm...

cross product "associative triples" Homework Statement We know that the cross product is not associative, i.e., the identity (1) (\vec{a}\times\vec{b})\times\vec{c} = \vec{a}\times(\vec{b}\times\vec{c}) is not true in general. However, certain special triples \vec{a};\vec{b};\vec{c} of...