Boat Crossing River

[@chereoge]

Phew!!! A video that finally explains this boat crossing river question. I had to go through so many unhelpful videos to find this one. Thanks a million.

[@yoprofmatt]

You are very welcome. Rivers are awesome! Cheers, Dr. A

[@jessemaretzki8002]

Dear Mr. Anderson, Thank you so much for this video. It really made the concept of dividing up problems into vectors clear to me. I am so grateful. Thanks so much!

[@yoprofmatt]

Great to hear. And thanks for the note. Cheers, Dr. A

[@hi4777]

dude, explained something better in 8 minutes than my teacher did in 1 week 💀

[@Chriss.lindstrom]

Just here to say thank you for uploading this. I see way too many videos that make this simple problem a lot more complicated. Thank you.

[@yuhankim2606]

I leave comments on youtube maybe every once in like a year. You explain 20x better than my professor

[@bloodyeyeful]

Last time I sank my canoe crossing a vicious current I was yelling "but the VRE is less than..."

[@goldenexperincerequiem638]

Hello sir You are a life saviour I am from foreign country I didn't actually understood from my mother-language and I was checking everything to understand this subject and I found you so thanks a lot sir now I can pass the exam hahah Have a good day/evening sir

[@StrangeQuark1.618]

Hello sir thankyou for your video but I have a question, what if the maximum speed of the boat is smaller than the velocity of the water flow and we have to find the angle theta and the speed of the boat relative to earth in which the boat has minimum horizontal displacement

[@StrangeQuark1.618]

Like such as river 5 m/s boat 3 m/s maximum speed

[@manuboker1]

Wonderful lecturer that makes physics fun and understandable !!!

[@Michelle-zb7gx]

Thank you so much!!!

[@tastewithsanai]

Thanks you sir! Atast I learnt it here! Huge respect from India 🇮🇳

[@yoprofmatt]

LOVE MY INDIA FANDERSONS! Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Use coupon code for India: FANDERSON2020INDIA Monthly subscription for 400 INR! Cheers, Dr. A

[@DT-zn9em]

Wow sir I really understood the problem so well I am able to do my problems in my textbook now thank-you!!! 🇮🇳🇮🇳🇮🇳

[@sps1053]

This is a great tool and you do a great job of explaining these concepts so thank you! I have one question. It seems like the students are sitting directly across from where you are facing and you are writing on the invisible board in such a way that everything is properly oriented for the students/viewers. Are you writing everything backwards or is there something in this set up I don't understand?

[@blitzeral8620]

i was thinking the same the whole video, he sure is skilled if he is writing all that backwards!

[@gnirrednow]

they obviously reverse the video before they upload it, wtf guys

[@SarveshKumar-ml5jd]

THIS VIDEO IS FLIPPED HE IS WRITING CORRECTLY

[@jamsamich2200]

YES he is writing backwards! by watching the video, you can tell that from his prospective he is writing from RIGHT to LEFT and not LEFT to RIGHT; however it also seems that he is writing letters and numbers backwards because that is the only way the students and the KZbin viewers can read the board from left to right without backwards letters.

[@jamsamich2200]

or there's some sort of screen/monitor that flips his writing in which the students have there attention on. whatever inverting system is capturing his lecture may also have the ability to record.

[@curtistrinh5654]

In case it is not clear, Solution(2), we use the theta= 30 and plug it into V_bR*costheta to find the vertical component/component crossing the river.

[@NZC_Meow]

What if the boat goes in a straight line? How far (angle) off track will it go from the straight line? Will the angle be equal to the angle we got here?

[@mjusticizer7171]

Hi Prof Matt. Thanks for uploading this video. Can you please explain another classic math/physics problem I till struggle on: Prove that the time taken in boating upstream after encountering an object floating downstream is the same as the time taken to turn back and boating downstream to reach the same object?

[@lurimay_jett]

I dont know if you managed to solve it, however here is the proof. Imagine the river distance is d, you start at d/2 for the sake of the problem. The velocity of the river is Vr, and the velocity of the boat is Vb, if you are boating upstream, you should have that Vb>Vr, in this case, imagine you are boating just a tiny bit faster than the river and it takes you t seconds to pass from d/2 (half the river) to d (the end of the river). If you solve, you have that Vb-Vr ≈ 0, and you have V=d/t, in this case Vtot=(d/2)/t, or 0=(d/2)/t. Now if you are boating with the current at the same speed Vb=Vr, then Vb+Vr=2, in this case Vtot=d/t, or 2=d/t. As you can see, if you solve for Vtot=(d/2)/t, you will end up with Vtot=d/2t, solving to leave t alone, 2=d/t, we can make this because we said that Vb>Vr and that is was ≈ 0 but not 0. I hope this makes it clear for you. So thats it, same time, upstream, is ≈ 0, distance is half, downstream is the same time, double the velocity, double the distance.

[@EMMANUELBOAFO-zz6lw]

I don't understand why he used sin for the horizontal component

[@sathwikakota7166]

I am from India . u r explanation of next level

[@khushigangwar2798]

jee aspirant?

[@Cassiro]

But if the boat rides perpendicular to the river's velocity, what is the boat's path?

[@chigo_e]

Thank youuuu!!!! Short and straight to the point...

[@AmIJorge]

Is this video mirrored or are you just a master of writing backwards? Edit: I have so many questions. What are you writing on? If you’re talking to a class and you’re facing them, how are they seeing what you’re writing? I was joking at first, but are you actually writing backwards??

[@roberttelarket4934]

What sort of glass blackboard is this for someone like me from the Stone Ages?

[@yoprofmatt]

Robert Telarket, Not writing backwards (I'm not that talented). The board is called Learning Glass. You can check it out at www.learning.glass Cheers, Dr. A

[@abdulrhmanalfawaz1885]

Probably the best vid this problem. Great job

[@paulproofmath323]

Please Mr. Anderson, why is the speed of the boat relative to the river greater than the speed of the boat relative to the earth?

[@yoprofmatt]

Paul Proof, Because it's working against the current. Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A

[@khushigangwar2798]

thank u professor it really helped me

[@WarHawk427]

I had more of a struggle telling whether you flipped the video horizontally after recording it than solving the problem. at 4:37 you hold up your right hand with a wedding ring on it...so I assume the video is flipped horizontally, but then you're calling on people in front of you to answer...so they can obviously see it too.

[@yoprofmatt]

WarHawk427, They have a monitor to view it. You might also like my new website: www.universityphysics.education Cheers, Dr. A

[@paulderrick8998]

Thank you so much, my teacher just said it’s a homework because he doesn’t even know how to solve it 🙏🏻🙏🏻

[@neelphsabiti6681]

Hi Sr the velocity of the boat was relative to the river not to the earth so I think you should first make both be relative to the earth

[@uyencao8176]

I love it , so helpful

[@mehikams7315]

Thank you so much sir. It's really helpful.

[@yoprofmatt]

You are most welcome. Cheers, Dr. A

[@lifeinoman4500]

Sir a question was like this in our exam- velocity of boat was given, width of the river was given, angle was given but velocity of current was not there. They asked what will be the velocity of the boat in the opposite direction of the current. How to answer this

[@denismakweba3870]

If a boat is moving downstream use dist=velocity × time But upstream take velocities difference v of river - v.current

[@anujkumar-xr8rn]

Can I get yo know which standard children learn this topic in England or america

[@carultch]

What do you mean by "which standard"? This class is a university level physics class in the USA. Usually a first year level class, but there are students who take it second year as well..

[@spiritualfoxplays-tryhardp2284]

Thank you so much sir!

[@surakdb9575]

why we get different answer by this equation Vbr=Vb-Vr

[@arjunkbiju3636]

Thank you professor...

[@yoprofmatt]

My pleasure. Cheers, Dr. A

[@TreyRhoton]

Does anyone know why he uses arcsin instead of arctan? I am using arctan quite frequently to find theta on several river problems; however, the angle is incorrect when I use it in this case.

[@ralisgroffen]

maybe because he wants to go across but the water goes perpendicular to it so it needs to go oblique, and in the other problems you want to go oblique and the water goes like at an angle so the boat needs to go perpendicular to the water to make it happen?

[@ralisgroffen]

you know other parts of the triangle i think

[@idowusamuelabel]

Well done 👏

[@mjusticizer7171]

It's still confusing because of the use of some jargons. Why not use simpler and easily understandable words like shore, water, still water velocity instead of earth, river and velocity of boat relative to river? Also need to explain, to be understood by laymen, why the velocity in actual direction is represented by V_BR.

[@carultch]

"Earth" is the first word that came to his mind. You could also call it the ground, the riverbed, the river bank, the shore, and many other words with the same meaning. Ultimately, it means the solid material beneath the river, that we consider stationary in this problem. He has a live audience who would ask for clarification, if his choice of words were beyond their vocabulary. The reason he uses the word velocity, is that it is a more specific word than "speed". Velocity means we are also interested in the direction, and not just the speed. The subscripts he uses for the various velocity values in this problem are the following: B = boat R = river water E = Earth / ground / shore / etc This means: V_BR = velocity of boat relative to river water V_RE = velocity of river water relative to Earth V_BE = velocity of boat relative to Earth

[@ralisgroffen]

me knowing the result of this example in 10 seconds, but not knowing how to do it with other numbers: I saw that the boat was twice as fast as the river, so in my had I 'calculated' the angle must be 30° because °-of-the-boat + 2-times-°-of-the-river must be 90°. Maybe a strange explaination, but I was correct.

[@jayrichard.]

Good thankyou

[@aldensova7537]

Many thanks, sir!

[@yoprofmatt]

You are very welcome. Keep up with the physics. Cheers, Dr. A

[@PHYSICSISEASY]

Very very thank you so much sir

[@yoprofmatt]

THE SUCCESS POINT PHYSICS CLASSES, You're very welcome. Glad you're enjoying the videos. You might also like my new site: www.universityphysics.education Cheers, Dr. A

[@NirajSingh-dw1ze]

Do you writing inversely in board and i am seeing accurate.....or t is technology

[@TheHiddenChronicle-b9l]

Niraj singh nope he is writing inversely no tricks no hackz

[@drnuzhatmustafa5000]

+Davis John 😆😆

[@VIZOR_AxK]

Niraj Singh he is not writing inversely, that is just the flipped image which is being shown to the students by monitors !

[@md.aminulislam3955]

whats happens if flow velocity is more than boat velocity ??

[@sanjayp.m7008]

The boat will never go to other end in practical situations:-) may be it would land in Pakistan though it intends to land in India:-)

[@carultch]

It would mean that you'd have to accept a downstream drift, if you were intending to cross the river this way.

[@PraveenSingh-cu2xe]

this is awesome sir

[@zaigamakhtar9237]

the uncanny Benedict Cumberbatch resemblance though.

[@sapnaaditya8477]

How can you write backwards really and you are clear good

[@yoprofmatt]

Thanks. Secrets revealed here: www.learning.glass Cheers, Dr. A

[@weiv6229]

a life saver TT

[@sofie9610]

demn he can write backwards 💀💀💀

[@jdeavraj97]

Shook... how can you write backwards!!!

[@yoprofmatt]

Not writing backwards. Check it out here: www.learning.glass Cheers, Dr. A

[@alanprakash6816]

thats cool sir

[@rexmastersh2625]

Right? right? 😂

[@rubayetnaser8585]

I've already done this math, Sir.

[@yoprofmatt]

Then you're way ahead of the rest of us. Cheers, Dr. A

[@hosseinazizi1426]

Velocity of boat relative to river you draw figure wrong and reverse

[@sanskarsrivastava7544]

Physicswallah follower 😁😁😁😁

[@yoprofmatt]

Sanskar Srivastava, Thanks for the comment, and keep up with the physics! You might also like my new website: www.universityphysics.education Cheers, Dr. A

[@SujanDahal]

Is anyone noticing that professor is writing in mirror image letters 😳😳😳

[@yoprofmatt]

I think they've notice. Secrets revealed here: www.learning.glass Cheers, Dr. A

[@jsanchez7467]

9Minutes to solve this, and teachers wonder why can't solve 15 of these questions in ~1hour

[@noahjohns3457]

how the fuck is he written in the opposite direction

[@deepakkumarverma5492]

what if Vre

[@splixmusic935]

Range of sin @ is from 1to -1

[@carultch]

If the river is flowing at a faster speed, than you can paddle the boat relative to the water, then it would be impossible to paddle directly across the water. At that river speed, the most you can mitigate the speed of the current is if you paddle directly against the current, in which case Vbe would equal Vre - Vbr, and you couldn't make any progress across the river. The fact that you end up with sin(theta) > 1, means that no real value of theta will allow us to solve this problem. If you know your complex analysis, and know how to solve sin(theta) = 2, as BlackPenRedPen will teach you how to do, then you will get complex numbers for theta, that are non-physical in this example.

[@drewbhardwaj]

Writing magic

[@yoprofmatt]

No magic. Secrets here: www.learning.glass Cheers, Dr. A

[@tamaleeeee]

woah he's writing backwards

[@donaalapatt5621]

Stupid🙄🙄🙄

[@upmanyughiya687]

Are hindi m bol yarrrr

[@adarshray39]

Lol there Is no student. The video is reverse and no one can read it without reversing it.

[@yoprofmatt]

There are, in fact, students there. Right next to the glass, we have monitors that are showing the flipped image. It's interesting that half the time the students are looking at the monitors, and the other half of the time they are looking directly at me through the glass. Cheers, Dr. A

[@skskk]

Will you be my physics teacher for 2018