Solution to Problem 215 - Nuclear Energy

[@liammccreary2941]

Thank you Professor Lewin. I first watched your MIT lectures on physics as a sophomore in high school. I have since received a bachelors in science in medicinal chemistry and worked for 5 years researching cancer. I have always dreamed of becoming a teacher, and just today I accepted a position teaching high school chemistry. Your lectures and problem-solving videos have been a constant companion in my love for science, and I consider them a guide for what makes a great teacher. Thank you for what you do. You inspire us all.

[@lecturesbywalterlewin.they9259]

thank you for your kind words - Great teachers are not born.

[@dashesi124]

Respect ❤ from Iran 🇮🇷

[@jumaaman6260]

Thank you Profesa. I admire the way you make physics more beautiful

[@lecturesbywalterlewin.they9259]

You're welcome, glad you like it.

[@rafaelpadilla757]

Really nice solution indeed Keith. Please Professor don't rule out more Nuclear Physics problems in the future, they are boring but they are not if taught by you

[@ishanbarma5413]

Wish you long life Sir. 🪷🪷🪷

[@lightsout4339]

I am exited to see your lectures on this branch of physics. I haven't started it yet

[@abulkhayer4898]

How are you Professor? It's been a while I'm watching you.....

[@shubhamp.]

He retired from MIT And he has a ton of research papers

[@Ryuga756]

I just brought one of the best physics book "For the love of physics" It was one of the best which made me fall in love for physics Thank you sir

[@lecturesbywalterlewin.they9259]

Glad you enjoyed it.

[@Kmrvoltage]

Sirs dedication 😮

[@santanuchatterjee654]

Sir, There are a few queries that I would like to ask you. It is not related to this video but friction. We study that friction is independent of area of the surfaces in contact, but then we also learn that rolling friction is less than sliding friction. Why is it so? During rolling, ideally only one point of the object is in contact. So hasn't area got any role to play here?

[@lecturesbywalterlewin.they9259]

watch my 8.01 lectures - *that's what they are for* your aswers are all there.

[@santanuchatterjee654]

@lecturesbywalterlewin.they9259 Alright Sir. I'll watch it and get back to you. Thank you Sir.

[@NavtejSingh-r3g]

You are a Legend ❤

[@AyanMobile-y1z]

You are the best ❤️❤

[@Tokito62257]

Ah I only forgot to account for the neutrons. My answer was 173 MeV. Thanks professor for the amazing questions.

[@lecturesbywalterlewin.they9259]

I counted you and others who overlooked the 8 MeV among the 5 winners

[@Tokito62257]

@@lecturesbywalterlewin.they9259 Thanks sir. I'm going to be trying your questions, as best as I can.

[@Tokito62257]

​@@lecturesbywalterlewin.they9259 glad to hear it, I was cursing myself for missing it when I saw the solution

[@Tokito62257]

@@lecturesbywalterlewin.they9259 And here I was cursing myself for neglecting those neutrons

[@Tokito62257]

And here I was cursing myself for ignoring those neutrons

[@ld238]

Found the mistake in my solution, inaccurate rounding. A neutron isn't 1.00 mass units u, but 1.009u. Thanks for sharing the correct solution!

[@lecturesbywalterlewin.they9259]

you are still confused - plse watch the solutiion again

[@ld238]

​​​@@lecturesbywalterlewin.they9259 I did it both ways, looking up masses m or binding energies E in the web. They are equivalent: E=mc^2. Both results in 174-8= 166MeV or in terms of mass loss 0.1866u when using the correct value for the neutrons. At my first attemt I got 0.203u = 188MeV due to careless rounding. (Why can't I use the masses?)

[@chillframe-t2y]

Sir i have always been wondering if e=mc² if small amount of mass can be converted to big energy then means is c = square root of e/m,,,is this possible

[@lecturesbywalterlewin.they9259]

question unclear - c has been *measured* to at least 9 digit accuracy. The speed of light is known with extreme accuracy, as it is defined as exactly 299,792,458 meters per second in the International System of Units (SI), meaning we know it with perfect precision because the meter is defined based on this value of the speed of light in a vacuum; essentially, we don't "measure" the speed of light, we use it to define the meter itself.

[@Auxiliary-v7e]

Professor Lewin, do you think that nuclear energy is a better alternative to green energy like solar and wind?

[@lecturesbywalterlewin.they9259]

solar energy is also nuclear energy

[@harishsrivastava078]

1)Why we are decreasing only the kinetic energy of three product neutrons to find the value of X and ignoring the Kinetic energies of barium and krypton nucleus? 2) X is the total amount of energy released which is in the form of radiation and kinetic energy of the product nuclei and neutrons. So to know X why we decrease the kinetic energy of product neutrons?

[@lecturesbywalterlewin.they9259]

*The 165 MeV that is released is largely the KE of Ba and Kr.* Google: "When Uranium-235 (U235) undergoes fission, the resulting Barium and Krypton nuclei typically have a combined kinetic energy of around 200 MeV (megaelectronvolts) after the fission event. "

[@ShreyanshPrasad-kl6gf]

Walter lewin sir i am great fan of your teaching And i love ur teaching skills You are inspiration sir I am 16yrs old , i first watched lecture in my 10th Pls reply sir so that this would be my greatest motivation of my life time sir please 🙏🏻

[@lecturesbywalterlewin.they9259]

You can watch all my 94 lectures!

[@zainab-rr2ur]

What on earth I was doing? 😬 I come to know about you today and I'm already a law student. I wish I've found your channel earlier. I was really good at physics. Sir now in my free time I'm watching your lectures. Lots of love and respect. You're a legend. Kindly give me some suggestions to improve my concepts more and more ❤❤

[@lecturesbywalterlewin.they9259]

I see many law students in my classes.

[@aapddd]

Ik ben benieuwd hoe de verkiezingen gaan verlopen bij jullie in Amerika. Groeten uit Hoorn.

[@lecturesbywalterlewin.they9259]

ik hou m'n hart vast - Trump will be a *disaster* voor de hele wereld

[@mr.gamingochallengi5492]

Greetings Sir, I am currently preparing for IIT-JEE and am stuck at a point in wave optics, that is Intensity directly proportional to slit width or is amplitude directly proportional to slit width (which would make intensity the square of Slit width). I tried solving PYQs also, and found that in certain questions former was used and certain others latter. Sir, I was unable to reach any satisfactory solution and didn't find any concrete result online. I will be really grateful, if you could solve this doubt if one should take Intensity proportional to Width² or Width. Thank you sir Yours Truly Anubhav

[@AubreyKun98]

Sir which lecture do i have to watch for JEE examination Physics. I think your lectures will help me kindly tell

[@lecturesbywalterlewin.they9259]

Watch all my 94 MIT course lectures. Start with 8.01, then 8.02, then 8.03. Do all the homework and take all my exams. *I guarantee you that you will then do very well on the Physics portion of any freshman college or JEE exam* You will find all information you need on this channel in three playlists "Homework, Exam, Solutions & Lecture Notes". 8.01 & 8.02 will each take about 200 hours, 8.03 about 250 hours.

[@AubreyKun98]

@@lecturesbywalterlewin.they9259 thank you very much for reply and guidance. This is life saver

[@oldtvnut]

Aha - I see my mistake now. By starting with the U236 nucleus, I ignored the fact that the creation of U236 from U235 and a neutron absorbs energy rather than having no energy transfer. Thus, I missed the -6.5 MeV in this first step. I had the right number for the difference between U236 and the final products, but not the over-all result.

[@lecturesbywalterlewin.they9259]

I still counted you as a of the 5 winners and also 3 others who overlooked the 8 MeV of the 3 neutrons

[@imRann-2.0]

Love you sir ❤️🇮🇳

[@GerlikasIgnotas]

Amazing video, thank you.

[@lecturesbywalterlewin.they9259]

my pleasure!

[@markitsche987]

We have a Fermilab near Chicago.

[@lecturesbywalterlewin.they9259]

ofcoz I know

[@oldtvnut]

The equation given in the problem statement includes all the products and an energy X. But then it says you need to look up the (kinetic) energy of the three product neutrons, and the solution posted says that X is the total minus the neutron's kinetic energy. I don't understand why the X in the equation does not include all the energy produced including the kinetic energy of the neutrons.

[@lecturesbywalterlewin.they9259]

watch the solution again

[@oldtvnut]

From world-nuclear org: "About 85% of the energy released is initially the kinetic energy of the fission fragments. However, in solid fuel they can only travel a microscopic distance, so their energy becomes converted into heat. The balance of the energy comes from gamma rays emitted during or immediately following the fission process and from the kinetic energy of the neutrons." It was not clear to me that X represents only the heat and gamma rays and not the kinetic energy of the neutrons.

[@lecturesbywalterlewin.they9259]

@@oldtvnut you are 1 of the 5 people who had the right answers. 4 of the 5 overlooked the 8 MeV of the 3 neutrons. I called them all winners. You are one of them.

[@oldtvnut]

@@lecturesbywalterlewin.they9259 Thanks. I remember learning the general principles involved, but not sure I ever had a numerical problem like this. This is fun to revisit and learn more.

[@Jordan-kk1rh]

Hi Walt.

[@02P9j]

Sir , I don't know you reply me or not ,But what your experience says about should I know much more about mathematics, I'm not good at mathematics but at physics I think I'm much good than an ordinary 11th grade student,at me physics is a language of the Universe it's can explain atom to universe ❤

[@lecturesbywalterlewin.they9259]

eat yogurt every day but *never om Fridays* That also worked for Eistein and me.

[@02P9j]

​@@lecturesbywalterlewin.they9259Is there any Video of yours where you explain how You learn and Studied at your student life ?

[@FaizanAli-i8r3i]

Sir please answer me how to remember physics please please please please please, 🙏🙏🙏🙏🙏🙏🙏 😢😢😢

[@lecturesbywalterlewin.they9259]

eat yogurt every day but *never on Fridays* That also worked for Einstein and for me

[@souravkhan4445]

Professor, I'm Sourav from India. I'm a physics graduate. 26yrs old. I'm working as a private tuition teacher of high school standard. I want to demonstrate all the experiments to my students. But there has two problems, one is cost of the experimental setup; second one is experimental knowledge in all chapters. I want a suggestions from you, if you know any book which can help me gain knowledge as well as demonstrate physics experiment using home's setup spending very few money.... Plz let me know.... If you allow me any other form of direct contact with you!,i will let you know what type of experiment I'm talking about & related chapter.... So that you can guide me.... Desperately i need this help. Touching your feet.... Have a good time professor....

[@lecturesbywalterlewin.they9259]

I suggest you watch all my 94 MIT course lectures and write down all de demos I have done. Typically 10 per lecture that is a total of about 1000 demos. Concentarte on those that do not require expensive equipment. My lectures are MuCHHHhHHh better than any book. You can only contact me on my channel. all the best

[@veenapandey5745]

HELLO PROFESSOR LEWIN. MY NAME IS VIDIT A HIGH SCHOOL STUDENT FROM INDIA. I HAVE A QUESTION WHICH HAS NOTHING TO DO WITH THIS VIDEO, IT'S JUST MY CUIRIOSITY THAT'S MAKING ME DO THIS . ONCE I WAS SLEEPING WITH MY FACE DUE SOUTH. A NUMBER OF MY FAMILY MEMBERS WENT AGAINST THIS THING AND ASKED ME NOT TO DO ANY KIND OF ACTIVITY BY FACING DUE SOUTH. WHEN I OBJECTED THEN THEY WERE READY WITH BOTH RELIGIOUS AND SCIENTIFIC ANSWERS. OFC I AM NOT GOING TO TELL U THE RELIGIOUS ONE BUT SCIENTIFIC. THE REASON THEY TOLD ME WAS THAT JUST LIKE THE EARTH OUR BODY ALSO HAVE POLES . AND DUE TO ATTRACTION BETWEEN POLES OF OUR BODY AND EARTH WE TEND TO LOOSE ENERGY. AS FAR AS MY KNOWLEDGE OF PHYSICS IS CONCERNED I HAVE NOWHERE SEEN THAT THERE HAPPENS LOSS IN ENERGY IN A MAGNETIC FIELD . WHAT ARE YOUR VIEWS ABOUT THIS. I AM EAGERLY WAITING FOR YOUR REPLY.

[@lecturesbywalterlewin.they9259]

question unclear - try Quora

[@veenapandey5745]

​@@lecturesbywalterlewin.they9259 Sir basically my question is that does earth magnetism state that a person should not do any kind of activity facing due South or North?

[@wotcherfaz]

Wow I didn't know krypton is a real element. I thought it was just a fiction in the superman story... doh.

[@lecturesbywalterlewin.they9259]

The *noble gases* are helium (He), neon (Ne), argon (Ar), *krypton (Kr),* xenon (Xe), radon (Rn)

[@carultch]

Krypton the element is real, and its name came before the name was also used in Superman. Kryptonite is fiction, and doesn't exist in reality, since Krypton is an inert gas. While chemists have been able to get Krytpon to bond in the laboratory, it is unlikely for it to form the oxygen bonds that would make Krytonite real.

[@bobbyrai8428]

Again first

[@Jee2026Aim]

He is old he ll not see this one

[@ILoveFunVR]

how are you still alive?

[@lecturesbywalterlewin.they9259]

I aleady died 3 years ago

[@ILoveFunVR]

???

[@OutlandishFacts]

Dear Professor Lewin, Thinking about the Fermi Paradox I was wondering if you’d be able to analyze the NASA STS-75 Tehter Incident. There seemed to be many orbs around the object when the tether snapped. I was wondering if it is physically possible for these particles to be debris considering their trajectory, shape, varying velocities as well as the shadows present? kzbin.info/www/bejne/qIrXn2minMmLnsk

[@lecturesbywalterlewin.they9259]

my friend, the astronaut Jeff Hofman, was onboard the Shuttle when this happened

[@OutlandishFacts]

@@lecturesbywalterlewin.they9259 That’s amazing!! Also happy belated birthday to him 🥳

[@Tom-yv9sc]

Dear professor, I eat yogurt every day, but why am I still not good at physics, is there something wrong?😅

[@lecturesbywalterlewin.they9259]

for how long have you eaten yogurt every day but *not on Fridays*

[@blueoryx101]

Gpod qn sir

[@Parth0047]

Sir we can talk about Thorium problems and discuss on their solutions 🧪