I used 5 seconds to think like this: The train must use 90/10 h = 9 h. The bird also travels for 9 hours. The bird´s speed is 3 times faster. So 90 x3=270
In the second case, Train 1 travels 30 km in 3 hr while train 2 travels 60 km in 3hrs. The bird also travels for 3 hrs, therefore we can say that the bird travelled 30*3 = 90 km
@@AmitAntony. no 150 is wrong because u took relative velocity of bird with the second train then u will have to take different cases coz initially vrel = 50 (30+20)but afterwards when birds direction changes relative vel changes so 150 is wrong...
instead of series addition, I did this by taking time as constant since time is same for both objects, time taken by train = 9hrs and the total distance traveled by the bird is t*s = d (9*30 = 270km)
The bird has constant speed so if we could know how long is the time of flight we can find the distance travelled and since the bird flies untill the trains collide so we can solve through relative velocity concept i.e. by finding time of collision , if we assume train A is at rest then train B is coming towards it at a velocity 30km/hr and since separation is 90km so train B will collide with train A in 90/30 = 3hrs , so bird will travel a ''distance" of 3*30=90 km
Hi Mahesh, Not sure if it's allowed on Khan Academy. But in your future videos there, please use this production style of you appearing in the intro on camera, before switching to your screen capture videos that y'all at Khan Academy do so well. It adds to the conversational tone, and helps establish a connect with the learner even if you're not talking to them real-time.
We don't do that because a) It breaks the Khan style established over the years, b) costs more resources and time to produce it. Our videos need to be localised in various languages, and the cost and total time of production would just explode!
@@Mahesh_Shenoy Thank you for explaining, Mahesh. Fully makes sense now. I guess camera on videos work for announcements. But for instructional content the Khan style works.
Solution for the challenge problem at 6:27 : Time taken for both trains to meet is 90/(10 - (-20)) = 3 hours In that time the, the distance travelled by the bird is (30 kmph)*(3 hours) = 90 km. Distances travelled by the bird to the right is an infinite geometric progression : 54, 5.4, 0.54, ... Using the infinite sum formula for GP total distance travelled to the right = 54/(1 - 1/10) = 60 km Which means the distance travelled by the bird to the left must be 90 - 60 = 30 km
That was a great explanation I have a question regarding the same problem : ‘How many trips will the bird make before it comes to the rest?’ How should we approach this question?
Fun fact: I am the 270th like This is the best simple question i have heard in my life , just see that train takes 9 seconds just multiply it by speed of bird, boom 270km.
90 kms as both the train will cover their distance in same time and the sum of their travelled distance is 90 so, if first train travel x kms then second one let y kms and we know that distance equals speed × time so , the first one will have 10t hr (say t as time taken which is equal in both the cases) and second will have 20t hrs now, 10t+20t must equals to 90 as x+y = 90 therefore t= 3 now as the time taken by the trains to approach each other equals to the time taken by the bird to move around them therefore speed=distance/time 30=distance/3 . . so , t= 90 hence distance travelled by the bird will be 90 kms....😀
Can you please explain this doubt- in certain quantities of cross product we define it as a × b . For eg in torque we define it as r × f and direction by right hand thumb rule but why can't we define it as f×r . I mean is it only a convention or there is logic behind it . Please answer this
Sir I know this is out of the context.....can u make a video about the process of making these amazing videos....like what and where all from do u collect information and come up with storylines and your equipments and stuff....
First we will find relative velocity that will be 30 And is same as the birds speed so the bird will travel same distance ie 90 Now time take to meet both of them will be distance by relative speed which will be 3 Then multiply 3 to right trains speed and we get 60km And to left we get 30km
Sir, please reply to me,sir please reply to me I know how mathematically and all that why the equivalent resistance of the parallel circuit decrease as we keep on adding resistors,and is always less than the value of the smallest resistors,but sir,Im not able to feel it,It is not just feeling natural learning that,can u please make a video with ur brilliant explanation skills to make it feel more natural? please sir,I highly beg from you, please sir
Sir , im a fan now , i request you please please please make more and more videos on +1 and +2 physics , they are liberating. And please suggest me some people like you to learn biology ,some more physics and chemistry from ,if u know someone. Thank you sir 👍
Sir,can u please clear one of my doubts, We know electricity is due to potential difference,but sir,what actually is potential energy?I have seen multiple videos of it claiming it to be the work done to move a charge from infinity to a point,but sir,even if this is true,how does this apply to battery?how is this related to a battery's potential difference?can u please explain here in the comments or even better,make a wonderful video of yours explaining it,thanks a lot sir
Wrt green train Yellow train has velocity 10 + 20 = 30km/h Bird velocity w.r.t train --: 30+20 = 50 km/h Since Now bird relative velocity = 5/3 of yellow train relative velocity So distance covered = 5/3 of distance covered by yellow train =5/3*90 =150 km answer
The challenge Q....................Here instead of 2 trains moving at 10 and 20km/hr(towards each other), we can apply the concept of relative velocity and consider it like 1 train travelling at 30km/hr.....and the distance is 90 km. As the bird also is travelling at 30km/hr we can say that the bird and train reach the station at the same time and the bird covers a total distance of 90km towards right. Since the bird reached the station the moment the train reached , it could not turn back and travelled 0 kms towards left.
Total 90, right =30 , left =60 Video was exceptionally crafted, Really enjoyed solving this problem, please bring more Puzzles and valueable lesson like this one.
I dont know why it is entitled as a hard one... Its reletively an easy problem... You just manipulate the equation for constant speed and get the answer... The intuition behind this is also very straight forward. Edit: Ahh neumann did the summation...shocked.. People can be so intelligent.
Two words - Click bait! Also, not really. For someone who is just learning about this, I don't think it's that straight forward. I was mind blown the first time I came across this problem!
if we solve the question from the train's frame of reference, i'm getting 180km as the answer, can anyone explain the fault in the solution? p.s. i understood the solution given in the video and agree with it i just want to know where went wrong.
I'm not too sure as to how you got 180km, but, just think of the green train being stationary wrt to the yellow train. So, the relative velocity of the yellow train is clearly 10+20 = 30km/h. Now, it would take 3 hours for the yellow train to cover 90km. Therefore, the bird has been travelling for 3 hours. So, it must have covered 3*30= 90km. The key part is that the bird's velocity is 30km/h wrt to the ground. We don't care about the velocities of the trains wrt to the bird, we just care about the TIME, since time passes in the same way, for both the trains, and the bird.
The bird stops moving when trains stop moving Trains stop movin after 3 hours cuz the total speed of the trains is 30 So the bird flies for 3 hours, 30 * 3 = 90
