Calculating relative velocity | Class 11 (India) | Physics | Khan Academy
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- Опубліковано 21 бер 2018
- How do we calculate the velocity of one object as seen by another object? In this video, we will intuitively figure out how to calculate relative velocities with some examples. We'll then write down the general expression for calculating relative velocity. Created by Mahesh Shenoy.
Why cant i hit the like button more than once??? Also thanks alot to save me from my physics test tommorow
Wow! Great explanation Sir Mahesh! Thankyouu!
Amazing tutorial thanks a lot man! 😊😊😊😊
Hi I have a doubt that in snail and train problem you considered that snail direction is positive and trains direction as negative hence you get a formula like Vst=Vs+(-Vt) but actually according to our textbook the direction of snail is
negative and train direction as positive ( like towards west positive and towards east negative) then we get formula as Vst= -Vs+Vt but if we take the general rule or formulae according to our textbook it's says if a object moves in same direction then Vab=Va-Vb and for opposite direction Vab =Va+Vb . Even though we get same answer which concept is like right ?
thanks really helps
Very perspicuous explanation. Though, I am a tad confused about the snail and train thing. In the example antecedent to the snail&train one, Usain Bolt and Aakash started off from the same point. So Bolt with 9m/s and Aakash 5 m/s means Bolt would have travelled 9m in a sec. But in the starting point he saw Aakash was at rest ( both were at rest at that moment ) and after a second, Aakash seems to have slid backwards by 4m. So -4m/s very much makes sense-because they both were at rest and same x coordinate position.
The initial distance b/w snail and train is something, as it can be seen from the video, so train after 1sec will travel 50 m from its initial pos. And snail will travel.... I mean.... I don't know what I should say. I'm bewildered.
I know you got what my doubt is. Thank you :) :) :)
The initial position is irrelevant. Say the distance between the snail and the train was exactly 52 meters when we started analyzing the situation. Then in 1 second, the train would move forward 50 m, and the snail, 2 m and they would end in the same position. Now from the train's perspective, it's at rest. So it would seem as if it's the snail that covered the entire 52 m in that 1 second. Does that make sense? You would get the same conclusion regardless of their initial positions.
Also a side note, maybe I should have been more clear about it, they are not at rest, to begin with. We have just 'paused' their motion. (You know so that we don't have to deal with acceleration and whatnot)
@@KhanAcademyIndiaEnglish Thank you. Just to make sure if I got what you said, that means if I am travelling in a car at a velocity of 21m/s on a straight road and I see a speck of house very very far away from my moving car, and my car keeps on moving with that velocity of 21m/s, the relative velocity of the house ( at rest ) is -21m/s? And its same at all instants if my velocity remains constant? And when I accelerate my car from 21m/s to 25 m/s the relative velocity of the house assumes values from -21 to -25 m/s?
So essentially relative velocity means how does the object in consideration seem to change position w.r.t to you, and you may or may not be moving? Pls check if I am correct or not.
Thank you
when yo use snail and tain then it will show -48m/s speed of snells
plz explain
Khan academy India,
In the case of snail wrt train , shouldn't the formula be Vst= Vs - (- Vt) = > Vs+Vt
Yes exactly. Thats why I am confused too.
look: the direction in which the snail is moving is positive and that of train is negative. You could have done it the other way round, too. The only thing that matters is that since the directions are opposite, so are the signs. Now, he said that the snail moved 2m in 1 second while the ground moved 50m in 1s in the same direction. Therefore he adds the velocity. But since the direction of the TRAIN is in the opposite direction, and in this case, negative, snail's velocity has been ADDED to the negative of the train's velocity. If you look at the final formula and put the values you would get relative velocity of snail w.r.t. train as 2-(-50)=2+50=52m/s. I hope I made sense.
The formula for snail w.r.t. train is wrong it should be Vst = Vs - Vt
So Vst = 2 - (-50) = 52
That's exactly the formula written. Check @7:31. Could you elaborate your doubt? :)
@@KhanAcademyIndiaEnglish bottom right corner says
Vst = Vs + (-Vt) the plus sign confuses me
Am I correct?
@@AnuragSingh-oc4gb Vs + (-Vt) = Vs - Vt. So I am still not sure where the confusion lies.
@@KhanAcademyIndiaEnglish
The problem is that the correct equation should be Vst = Vs - ( -Vt)
Not Vst = Vs + (-Vt)
Khan academy india has less accent than it has for ireland