If we are in a free fall which implies we are accelerating at 9.8 m/sec every sec. And let's say that we are falling into a pit that has enormous depth. So isn't this be possible that we may accelerate and surpass the magnitude of speed of light?
In Newtonian mechanics, if we throw an object in against direction of gravity with speed $v$ and it achieve max height of $h$. Now if we allow object to fall from that height $h$, it will eventually attain speed $v$ when it reach position where we launch it.   Now applying same idea to a black hole in general relativity. Speed require to escape black hole gravity is greater than $c$, so if we throw something into black hole with almost the speed of light, the object speed will exceed speed of light $c$ before hitting black hole surface! How relativity explain this? Can space-time curvature reduce speed of this freely falling object from attaining speed of light?
How can I find out which process is locking a file or folder in Windows?  For instance, when trying to delete a folder, Windows reports this:     The action can't be completed because the folder is open in another program   Happens the same with a file, but how do I find out what program or application is currently using it and preventing me from deleting the file or folder? Measuring the distance between lines and points in QGIS Using QGIS - I have a vector of fault lines.  I have point data in the form of a csv which I have also loaded into QGIS.  I need to know how far each point is from the nearest fault line then enter this distance in a new column in the csv file. Any ideas? What does echelon mean? When you solve a system of linear equations, you write down the augmented matrix and reduce this to reduced row echelon form. What is the meaning of the word echelon? See all shared items in Google Drive In Dropbox there is a place you can see all the shared items in your account (i.e., all the items you have granted others access to).  Is there a similar feature in Google Drive?  I'm not only trying to find items that are shared with other "named people", but also documents that are shared on a "anyone with link can view / edit" or "public on the internet" basis.   Franck's  seemed to work back in 2013, but Google Drive's interface has changed quite a bit since, and I'm struggling to be able to perform the same task with the new interface. I wonder if anyone knows how to do it in the new interface. How can I get distribution name and version number in a simple shell script? I'm working on a simple bash script that should be able to run on Ubuntu and CentOS distributions (support for Debian and Fedora/RHEL would be a plus) and I need to know the name and version of the distribution the script is running (in order to trigger specific actions, for instance the creation of repositories). So far what I've got is this:  OS=$(awk '/DISTRIB_ID=/' /etc/*-release | sed 's/DISTRIB_ID=//' | tr '[:upper:]' '[:lower:]') ARCH=$(uname -m | sed 's/x86_//;s/i[3-6]86/32/') VERSION=$(awk '/DISTRIB_RELEASE=/' /etc/*-release | sed 's/DISTRIB_RELEASE=//' | sed 's/[.]0/./')  if [ -z "$OS" ]; then     OS=$(awk '{print $1}' /etc/*-release | tr '[:upper:]' '[:lower:]') fi  if [ -z "$VERSION" ]; then     VERSION=$(awk '{print $3}' /etc/*-release) fi  echo $OS echo $ARCH echo $VERSION   This seems to work, returning ubuntu or centos (I haven't tried others) as the release name. However, I have a feeling that there must be an easier, more reliable way of finding this out -- is that true?  It doesn't work for RedHat. /etc/redhat-release contains : Redhat Linux Entreprise release 5.5  So, the version is not the third word, you'd better use :  OS_MAJOR_VERSION=`sed -rn 's/.*([0-9])\.[0-9].*/\1/p' /etc/redhat-release` OS_MINOR_VERSION=`sed -rn 's/.*[0-9].([0-9]).*/\1/p' /etc/redhat-release` echo "RedHat/CentOS $OS_MAJOR_VERSION.$OS_MINOR_VERSION" And now I am unable to chmod it back.. or use any of my other system programs. Luckily this is on a VM I've been toying with, but is there any way to resolve this? The system is Ubuntu Server 12.10.   I have attempted to restart into recovery mode, unfortunately now I am unable to boot into the system at all due to permissions not granting some programs after init-bottom availability to run- the system just hangs. This is what I see:  Begin: Running /scripts/init-bottom ... done [   37.062059] init: Failed to spawn friendly-recovery pre-start process: unable to execute: Permission denied [   37.084744]  init: Failed to spawn friendly-recovery post-stop process: unable to execute: Permission denied [   37.101333] init: plymouth main process (220) killed by ABRT signal   After this the computer hangs. I'm trying to install  in VirtualBox but the installation get stuck at Do you want to install boot loader GRUB    Some background:   The VM was created from the Ubuntu 32-bit (x86) VirtualBox template The VM has 1 core + 3096 MB RAM Video memory: 32 MB PAE/NX enabled Hardware virtualization: both VTx and nested pagination enabled Graphics acceleration: disabled (both 2D and 3D) Storage: 64 GB attached to IDE virtual controller (was SATA before: makes no difference)   I've already tried all the "standard" VirtualBox procedure (PAE yes/no; SATA/IDE; no soundcard; no USB; graphics accel. yes/no).  I also tried run the Live CD in VESA mode: like this it starts, but I'd still prefer to install it. I have the below list of files  aro_tty-mIF-45875564pmo_opt aro_tty-mIF-45875664pmo_opt aro_tty-mIF-45875964pmo_opt aro_tty-mIF-45875514pmo_opt aro_tty-mIF-45875524pmo_opt   that I need to rename to  aro_tty-mImpFRA-45875564pmo_opt aro_tty-mImpFRA-45875664pmo_opt aro_tty-mImpFRA-45875964pmo_opt aro_tty-mImpFRA-45875514pmo_opt aro_tty-mImpFRA-45875524pmo_opt Find $\lim_{n\to \infty}({1\over \sqrt{n^2+1}}+{1\over \sqrt{n^2+2}}+\cdots+{1\over \sqrt{n^2+n}})$ strong textFind $\lim_\limits{n\to \infty}\left({1\over \sqrt{n^2+1}}+{1\over \sqrt{n^2+2}}+\cdots+{1\over \sqrt{n^2+n}}\right)$. I do know it is bounded by $1$. I tried using the sandwich rule with no success. How can I solve it? Bash/Korn shell script edited on Windows throws error '...^M: not found' I wrote a Bash script in Windows using Notepad++.  cxStopAllServicesOnSERVER.sh  #!/usr/bin/bash cd "/some/path" echo "Hi. Logs can be found at "`pwd`"/cxStartStopLogger.log" echo "["`date`"]*** STOPPING ALL SERVICES ON SERVER ***" &gt;&gt; "cxStartStopLogger.log" exit   Now after uploading it and setting the required file permissions, I tried executing it as follows:  bash-3.00$ cat cxStopAllServicesOnSERVER.sh #Let's have a look at the code. #!/usr/bin/bash cd "/some/path/" echo "Hi. Logs can be found at "`pwd`"/cxStartStopLogger.log" echo "["`date`"]*** STOPPING ALL SERVICES ON SERVER ***" &gt;&gt; "cxStartStopLogger.log"  bash-3.00$ # Code and hashbang 'looks' correct,  bash-3.00$ # if there is any issue with the format (EOL characters and such)  bash-3.00$ # we cannot see it using cat. bash-3.00$  bash-3.00$ sh cxStopAllServicesOnSERVER.sh cxStopAllServicesOnSERVER.sh[2]: /some/path^M:  not found Hi. Logs can be found at /some/path/cxStartStopLogger.log bash-3.00$ # Note that ^M appears at the end of the line.  bash-3.00$ bash -x cxStopAllServicesOnSERVER.sh + cd $'/some/path\r' : No such file or directory1.sh: line 2: cd: /some/path ++ pwd ' echo 'Hi. Logs can be found at /some/path/cxStartStopLogger.log Hi. Logs can be found at /some/path/cxStartStopLogger.log ++ date + echo '[Sun' Nov 18 00:28:17 EST '2012]*** STOPPING ALL SERVICES ON SERVER ***' bash-3.00$ # Note that '\r' return character appears at the end of the line.   Problem: When I change the code to korn shell I face the same issue. Appears that an incorrect character is getting added at the end of the line.   NOTE: I found the solution and have posted the same as an answer. Feel free to update or improve it to help other beginners that may face the same issue.  Thanks! I am a beginning indie developer, and I want to get the word out about my game. What sites can I go to to ask about reviews of my game, and where might I be able to talk about and get feedback on my game from players? I'm using python in QGIS. I have a layer of polygons (its a result of some earlier dissolving and has no overlapping polygons but some holes and islands in holes etc). I want to build a new layer which contains one polygon representing a bbox of the first layer with each polygon cut from it.  Essentially I want to "invert" the layer I have so that where the was polygon, now there is not, and where there was not polygon now there is. All inside a bounding box of the original layer.  I can build a bbox easily and I tried to "subtract" the polygon layer from my new bbox polygon layer but the process slows to a stop and then crashes my PC. Here's the algorythm  processing.runalg("qgis.difference","path/to/polygon.shp","path/to/bbox.shp","path/to/result.shp")   I dont care about attributes (obviously). I just need to cut one set of polygons from one larger polygon.  It seems so simple, I wish I could find a simple command or script to acheive this. As stated at the top I'm looking for a solution in python in QGIS. Is there a recursive version of the dict.get() built-in? Special Relativity - Regarding the Simultaneity of Events During the Train Paradox My questions concerns that classic train paradox, wherein there is a train and a tunnel of equal length, and the train is traveling and some fraction of the speed of light towards the tunnel.  According to the Special Theory of Relativity, an observer outside the tunnel will see the train length contracted (Lorentz Contraction), whereas an observer inside will see the tunnel contracted.   Additionally, suppose that there were doors at the ends of the tunnel and that the observer outside the tunnel closed both doors instantaneously when he/she saw that the train was completely inside the tunnel.  The classic resolution of this paradox invokes the non-simultaneity of events, explaining that the observer in the train sees the far door close first, and then, once the train has begun to exit the tunnel, looks back to see the door at the beginning close. Thus, both observers agree that the train does not touch the door when they are closed for an instant.  Now my questions.  Why is it that the observer on the train sees the far door close first? It seems to me that the information coming from the far door would reach the observer on the train only after the information from the other door is reach.   Under this interpretation, the observer on the train would observe the train getting hit by the doors. What if, by some means, this event can be explained in terms of a stationary observer too? Everyone always concludes that the train remains untouched by the doors, but really the only condition that needs to be met is that both observers must agree. Why can't they both agree that the train was hit?  So, to summarize.   Why is the door that is farther away from the train observed to close first? Why can't the other possible conclusion (both see a hit train) be observed? No border-spacing before first item and after last item Most efficient way to concatenate strings? What's the most efficient way to concatenate strings? Prove that if $a \mid b$ then $\gcd(a,b) = |a|$ How do I grep for all non-ASCII characters? I have the need to synchronize the data in certain Salesforce tables (user, account, opportunity, lead, task, contact, etc.) to a local database. For reasons that I won't go into here, I can't use the streaming API. I want to kick off a local process every X minutes that will:   Go through each of the tables on my list Insert any new records Update any existing records that were updated Delete any records locally that were deleted on the server (either deleted directly or indirectly (e.g. through a foreign key relationship, like when an account is deleted its associated tasks are deleted as well).   Can you please offer advice on what API's might be good to use here, and whether one stands out more than the others? Are there any specific design recommendations that might be useful for achieving this goal? Or is there really no practical difference between what REST vs SOAP can do?  It comes down to what is the easiest to maintain/implement? Is there some other route that might be beneficial to use (example: bulk data load to start out followed by outbound messaging tied to all of the objects in question to get updates/inserts/deletes)?   I am using C#/.net. Ways to eliminate switch in code