Why is momentum conserved in an inelastic collision and kinetic energy is not conserved?
How can momentum but not energy be conserved in an inelastic collision?
When saving a .qgs file in QGIS, another appears. Is this a backup? When saving a project file (.qgs), which when executed is automatically loaded with qgis.bat, there's another .qgs file which appears in the same directory of the original project file, although this one is not loaded with the qgis.bat file:    This is just out of curiosity but is the latter designed to be a backup of the original .qgs file? How come unpolarized light does not undergo destructive interference? As far as I know, unpolarized light is defined as light which has no clear axis of polarization, but electric field vectors in all directions. However, I also know that electric fields can be superpositioned. So this leads me to the conclusion that if unpolarized light has equal $\vec E$ vectors in all directions, they should cancel.   Obviously, though, this is wrong (we've got light!). What's the explanation? Calculate $E(X^{2n})$ where $X$ is normal (0,1) I need help proving the following:  Let $X$ be normally distributed with parameters $\sigma=0$ and $\mu=1$. Let $n$ be a positive integer. Show that:  $$E(X^{2n})=\frac{(2n)!}{2^nn!}=:(2n-1)!!$$  I've tried the change of variables $Y=X^2$ and then calculating the integral, but got nowhere. Any hints?  Thanks in advance! I cant use lhopital's rule here is my attempt:  Limit of $(\frac{n^{2}-2n+1}{n^{2}-4n+2})^{n}$ =$e^{\lim_{n\to \infty} n\times \ln(\frac{1 -2-n +\frac{1}{n^{2}}}{1 -\frac{4}{n} +\frac{2}{n^{2}}})}$ I got stuck here I'm attempting to build an LED bed lamp that will be powered by 240V mains. The LEDs are  which if I use with a 12V supply and have calculated correctly will draw 0.24W each. I plan to use 5 or 6 of them in the lamp so will consume a maximum of 1.5W.  Initially I thought I'd use a transformer and bridge rectifier to get the required 12V DC but the transformer weighs a ton and is too bulky. The next option was to use a  but I'm wondering is there is a better way?  I think it would be possible to power the LEDs directly from mains using only a rectifier without mains and stepping down the voltage but then it's not safe. Are there any smallish components that can both isolate the mains and supply a DC voltage? I can't figure out how to line up the symbols of an itemize environment in beamer with the left part of the main text. In other words, I would like to supress the left margin in beamer itemize lists.  It would be nice if the solution worked with any itemize label defined with  \setbeamertemplate{itemize item}[]   In order to make myself clearer, what beamer produces by default is something like:  Main text. Main text. Main text...    * Item 1    * Item 2    * Item 3    ....   and the desired result is   Main text. Main text. Main text... * Item 1 * Item 2 * Item 3 .... sum of noncentral Chi-square random variables I need to find the distribution of the random variable  $$Y=\sum_{i=1}^{n}(X_i)^2$$ where $X_i\sim{\cal{N}}(\mu_i,\sigma^2_i)$ and all $X_i$s are independent. I know that it is possible to first find the product of all moment generating functions for $X_i$s, and then transform back to obtain $Y$'s distribution. However, I wonder whether there is a general form for $Y$ like the Gaussian case: we know the sum of independent Gaussian is still a Gaussian, and thus we only need to know the summed mean and summed variance.   How about all $\sigma^2_i=\sigma^2$? Will this condition make a general solution? sequence $x_{n+1}=x_n+e^{-2018x_n}$ How to transit through Delhi without a visa? I have read a lot on this subject on the Lonely Planet forum and it looks like the staff on ground can transfer your bags through the Delhi airport if you have a connecting flight without you having to go out to check them in again and therefore needing a visa. I refer of course to the situation when you go with 2 different airlines, because otherwise the luggage is transfered automatically.  I posted a  and mentioned it briefly there, however I think this subject deserves a separate question and a detailed answer.  Does it depend on the type on an airline? I have read that Jet is no problem, what about AirIndia and IndiGo? And what about the incoming flight to Delhi from Europe or USA, do they all can hand over you luggage to the Indian airlines and pick it up again on the way home? Do you have to contact them before and explain your situation? Or check in your luggage directly to your desired destination? "Z-level" in TikZ In SF1, Stop refreshing the embedded vf page on a layout Below is my VF page which is embedded on a layout. In SF1 mobile app, it's getting refreshed whenever we touch on it. How can I avoid refreshing the VF page while touching it on the screen? In Desktop it's working fine. Please provide your inputs. &lt;apex:page standardController=&quot;PremiseObj__c&quot; lightningStylesheets=&quot;true&quot;&gt; &lt;apex:includeLightning /&gt; &lt;apex:slds /&gt; &lt;div id=&quot;premiseServDetails&quot;&gt; &lt;/div&gt; &lt;script&gt; window.onload = function (){     $Lightning.use(&quot;c:PremiseObjUpdateApp&quot;, function() {         $Lightning.createComponent(&quot;c:PremiseObjUpdatecmp&quot;,                                    {                                         recordId : &quot;{!Premiserecord__c.Id}&quot;                                     },                                    &quot;premiseServDetails&quot;,                                    function(cmp,event) {                                        setTimeout(function() {                                            //document.getElementById('loading').style.display = 'none';                                        }, 3000);                                    });     }); } &lt;/script&gt; &lt;/apex:page&gt; If $\phi$ is a homomorphism from the group $G$ with identity $e$ to the group $G'$ with identity $e'$, then $\phi$ is injective if and only if $\ker\phi=$?  I think the $Ker\phi = \{x\in G:\phi(x)=1\}$  because you are looking at an identity then it is all reals $0$ does not work a because if $x=0, e'x=0$  but then i realize it is injective how does that affect the kernel? Why can I see the output of background processes? For example, when I type ping 8.8.8.8 &amp;, why can we see ping process working? And when I type find / -name '*test*' &amp; , it's also seen on monitor.  Why is that? Is it not really in background? When will my device get the Android 4.2 update (Jelly Bean)? View linked Excel 'Windows' on separate screens Percentage of overlapping regions of two normal distributions I was wondering, given two normal distributions with $\sigma_1,\ \mu_1$ and $\sigma_2, \ \mu_2$   how can I calculate the percentage of overlapping regions of two distributions? I suppose this problem has a specific name, are you aware of any particular name describing this problem?  Are you aware of any implementation of this (e.g., Java code)? bug with varargs and overloading? What does "static" mean in C? $$\sum_{n = 1}^\infty \frac{(-1)^n}{p_n}$$ where $p_n$ is the $n$th prime.  I have computed this to 10000 rather than infinity. My results suggest that convergence does happen but it's very slow. But I can't even be sure about the first few digits: $-0.26959$?  I have looked at the "questions that may already have your answer" and some of the "similar questions," but they involve somewhat different formulas. If $a > b$, is $a^2 > b^2$? Given $a &gt; b$, where $a,b ∈ ℝ$, is it always true that $a^2 &gt; b^2$?