I was trying to solve a simple problem regarding a particle being launched by an angle theta where it hits a rod, we have: a) System(Particle, Rod) b) System(Particle, Rod, Henge)  My question is when will the angular momentum in each of the systems is conserved and is the linear momentum in any system conserved? And why?  I'm taking this course online, so if anybody could give me a rigorous and an intuitive explanation of what's going on it eould really mean alot to me. Thank you alot for your time Image:
Suppose we have a situation like      A ball of some mass $m$ with some velocity collides with rod hinged at point $A$. Is momentum conserved in this situation? I know that hinge will give impulsive force on rod but that is internal force when we take ball and rod together as a system so that shouldn't stop us using conservation of momentum equation
Restrict the access to suggested edit reviews on deleted posts on an answer deleted as rude/abusive is visible, even without logging in (and for users with less than 10k reputation). These users can't see the answer , via the , or a direct link to the .    This is a potential avenue for spammers, just like the suggested edit spam used to be, but is ; according to the :     In addition, in order to reduce the incentive for spammers to make spam edits that get rejected, suggested edit spam is hidden from logged-out users, so they can't show their clients public-facing pages with spam (so they won't get paid).   For this to work, the spammer would need two accounts, one to post the spam and a second one to suggest an edit. Even if the spam post is quickly nuked, the review link will be active forever. One could argue that logged-in users without 10k reputation shouldn't be able to see the suggested edits either; I'm partial to that. General term of Taylor Series of $\sin x$ centered at $\pi/4$ How can standing waves be produced in an open organ pipe if the ends are open? How can standing waves be produced in an open organ pipe even though both of its ends are open? Can someone explain with more clarity? Blender 2.8 - AWS EC2 command line EEVEE render I have been trying to get this to work for a couple days now. I have an EC2 P2 instance with NVIDIA CUDA configured by default, its a Deep learning Ubuntu AMI. This OS does not have a GUI so everything is via terminal.  I downloaded Blender's 2.8 TAR file for Linux and set it up on the EC2 instance. And ran the following command from the directory where the TAR file is extracted:   ./blender -b -noaudio /home/ubuntu/file.blend --render-output . --engine BLENDER_EEVEE --render-format PNG --verbose 4   All I see in the output is this:  Blender 2.80 (sub 75) (hash f6cb5f54494e built 2019-07-29 17:17:04) found bundled python: /mnt/blender/blender-2.80-linux-glibc217-  x86_64/2.80/python Read blend: /home/ubuntu/file.blend  Blender quit   Don't know why its quitting but I am unable to debug this any further. Any help would be appreciated.  UPDATE: As per @rjg's recommendation, ran the following command:  ./blender -b -noaudio /home/ubuntu/file.blend --render-output . --engine BLENDER_EEVEE --render-format PNG -f 1 --verbose 4   Got the following error:  Blender 2.80 (sub 75) (hash f6cb5f54494e built 2019-07-29 17:17:04) found bundled python: /home/ubuntu/blender/blender-2.80-linux-glibc217-  x86_64/2.80/python Read blend: /home/ubuntu/file.blend Unable to open a display Aborted (core dumped) Occasionally, you can see little tufts of leaves blowing in spots on the map      Do these mean anything? Where and how can I view skype logs (Chat and Voice history)? Where and how can I view my skype logs (Chat and Voice history)? Does it get saved somewhere in PC by default? Can I choose a folder location myself to start saving voice and chat history? I am trying to modify output in my twig file. In D7, I was able modify data in my array with this  check_markup($tweet-&gt;text, 'full_html');   and I see that this function still exists in D8. However, I'm not sure how I would use this in a filter in twig. This is what I have so far:  {% for tweet in params.tweets %} &lt;div class="tweet-wrapper"&gt; &lt;div class="tweet-profile-image"&gt;     &lt;img src='{{ tweet.user.profile_image_url }}'/&gt; &lt;/div&gt; &lt;div class='tweet-text'&gt;     &lt;!--check_markup($tweet-&gt;text, 'full_html');--&gt;     {{ tweet.text }} &lt;/div&gt;   &lt;/div&gt; {% endfor %}   I actually tried to do this before I sent it to the template as well, but it didn't change anything:   foreach($tweets as $tweet) {   $tweet-&gt;text = check_markup($tweet-&gt;text, 'full_html');   $cleanTweets[] = $tweet; } dpm($tweets); $params = array('tweets' =&gt; $cleanTweets); $tweet_template = array('#theme' =&gt; 'twitter_pull_tweet_listing', '#params' =&gt; $params); return $tweet_template;   What I'm trying to do here is make drupal create links for web links in the twitter tweet text. This worked fine for me in D7. I exported a map and everything looks fine when viewing the PDF. But when printing it on my plotter, all the text disappears. The scale bar would bring but the text associated to the scale bar wouldn't. The title block also disappears. I've tried messing around with the settings. I've checked/unchecked &quot;Embed All Document Fonts&quot; and &quot;Convert Marker Symbols to Polygons&quot;. I'm not sure what I'm doing wrong here. What's weird is I exported this map a few weeks ago and it printed just fine. Today, I needed to make a change to the map and exported it out, and now I am experiencing this issue. I must have changed one of the export settings in the past few weeks but I'm not sure what it is. Has anyone experienced this? Get the last item in an array Does $\sum\limits_{k=1}^n 1 / k ^ 2$ converge when $n\rightarrow\infty$? I can prove this sum has a constant upper bound like this: $$\sum_{k=1}^n \frac1{k ^ 2} \lt 1 + \sum_{k=2}^n \frac 1  {k (k - 1)} = 2 - \frac 1 n \lt 2$$ And computer calculation shows that sum seems to converge to 1.6449.  But I still want to know:  Does this sum converge? Is there a name of this sum (or the series $\frac{1}{k^2} $)? Trying to find the original story (I read it in Russian translation, original was most likely English unless it was Lem).  The story plot had artificial birds designed to serve as cops. The birds started attacking humans who were percieved as being aggressive towards anything alive. So they created more advanced birds to protect against the first ones. This worked for a while until the second kind started attacking humans as well. It ended with the idea that they would need another generation to attack the second-generation birds.  The story wasn't very long. I read it a while back (mid-1980s, which means the original was written even earlier, probably before 1980).  Despite a somewhat Asimov-like "misbehaving robots" topic, I'm pretty sure it wasn't Asimov. Why does this excerpt say that unbiased estimation of standard deviation usually isn't relevant? Three linked question on non-negative definite matrices. 1.a symmetric matrix in $\mathbb{M}_n(\mathbb{R})$ is said to be non-negative definite if $x^Tax≥0$ for all (column) vectors $x\in \mathbb{R}^n$. Which of the following statements are true? (a) If a real symmetric $n\times n$ matrix is non-negative definite, then all of its eigenvalues are non-negative. (b) If a real symmetric $n\times n$ matrix has  all of its eigenvalues are non-negative , then it is non-negative definite. (c) If $ A\in \mathbb{M}_n(\mathbb{R})$, then $AA^T$ is non-negetive definite. 2. only one of the following matrices is non-negetive definite. Find it. (a) $\begin{pmatrix} 5 &amp; -3 \\ -3 &amp; 5 \end{pmatrix}$. (b) $\begin{pmatrix} 1 &amp; -3 \\ -3 &amp; 5 \end{pmatrix}$. (c) $\begin{pmatrix} 1 &amp; 3 \\ 3 &amp; 5 \end{pmatrix}$.      3.let $B$ be the real symmetric non-negative definite $2×2$ matrix such that $B^2=A$ where $A$ where is the non-negetive definite matrix in question $2$.write down the characteristic polynomial of $B$.      My thoughts..  For1.  (a) &amp; (b) are true but not sure about (c). For 2. (a) is the correct option since it has all positive eigen values.they are $2,8$. For 3. Eigen values of $B$ will be $\sqrt{2}$ and $\sqrt{8}$. So the answer is $x^2-3√2x+4=0$.      Can anybody help me to verify the solutions of the above problems. I'm trying to identify a book I read in school, though I can't recall at what grade level; let's say it had to have been published before I graduated high school in 2000. Despite being required reading, it didn't feel much like a classic.  The story took place on Earth, after some catastrophe had caused the air to become poisonous. However, one teenage girl was able to survive because her house was in a valley which was somehow protected from the poisonous winds and was able to sustain its own ecosystem. One day, a man wearing a protective full-body suit and gas mask appears in the valley, and both are rather surprised to find someone else alive. She feeds and shelters the man and shows him how she had come to survive in the valley. Rather abruptly…      the man attempts to rape her, but she overpowers him somehow. She steals his protective suit and starts to leave the valley. He tells her that he had seen birds in a certain direction away from the valley, indicating there might be life there as well, and she leaves.   I believe there was an author's note either at the beginning or end of the book stating that the author had actually died while writing the manuscript, and that their friends or family had finished the book by going off the author's original notes, which I suppose may explain the abruptness of the ending.  In case it wasn't clear from the above, I didn't really like the book. But I'm curious about it regardless. Locking a file in Python Can we insert or update FieldSets using apex code? I understand that multivariate regression models contain more than 1 dependent variable, but what is the difference between running a multivariate regression with dependent a and b to a set of independent variables, rather than running two regression models, one for a and one for b against the same set of independent variables? I have a filename in a format like:     system-source-yyyymmdd.dat   I'd like to be able to parse out the different bits of the filename using the "-" as a delimiter. Is it possible to have connecting loop lines (like algorithm2e) in algorithmic? Why doesn't running "sudo shutdown now" shut down?