Calculating relative velocity | Class 11 (India) | Physics | Khan Academy

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.

[kevinsanthosh]

Why cant i hit the like button more than once??? Also thanks alot to save me from my physics test tommorow

[soumil]

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 :) :) :)

[alirazi]

Khan academy india has less accent than it has for ireland

[sowmiyashree]

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 ?

[Hino_]

Wow! Great explanation Sir Mahesh! Thankyouu!

[ankitshil]

Amazing tutorial thanks a lot man! 😊😊😊😊

[AnuragSingh-ocgb]

The formula for snail w.r.t. train is wrong it should be Vst = Vs - Vt
So Vst = 2 - (-50) = 52

[harshinidavuluri]

Khan academy India,

In the case of snail wrt train, shouldn't the formula be Vst= Vs - (- Vt) = > Vs+Vt

[brikham]

when yo use snail and tain <relative motion> then it will show -48m/s speed of snells