Physics 7 Relative Velocity (2 of 11) Linear Motion

[@justinfoto]

If you're confused about when to use addition or subtraction, I came up with an alternate way to think of these problems so I'll just put it here in case it helps anyone: Instead of a mix of addition and subtraction, you can think of it all as addition. Say "V_x/y" is the velocity of x relative to y. For this problem you could write it as: V_a/t1 + V_t1/g (g for ground) + V_g/t2 + V_t2/b = V_a/b Notice everything is addition and every "denominator" in the subscript is "cancelled" by the next term's "numerator" subscript. For V_g/t2, it may be difficult to think of the ground moving relative to the train, so can equivalently write it as -V_t2/g. Same goes for V_t2/b. Therefore with substition of the last two terms you get: V_a/t1 + V_t1/g - V_t2/g - V_b/t2 = V_a/b. Which is the same equation as what the professor got.

[@nroy15]

Justin Huang can u plz make a short video on that.. taking different cases?

[@md.saifulislam8607]

Your teaching is best....respect u......plz change your camer focus

[@MichelvanBiezen]

Yes, with our newer videos, we correct the focus with each video.

[@veenashan7504]

Why do you have to subtract the two values? Is there a reason for that?

[@MichelvanBiezen]

+Veena Shan Subtracting is one method to compare one value to another. Let's say you have two paths to a location. One is 20 km and the other is 25 km. If you want to figure out how much farther one path is compared to another you subtract the two values.

[@veenashan7504]

Oh that makes sense, thank you very much!

[@patrickmoloney672]

Great explanation.

[@thvyngvyen]

Do we have any video that talks about frame of reference in relative motion such as Earth frame reference, zero reference, etc.. Thank you very much.

[@MichelvanBiezen]

Only in terms of special relativity. See playlist: PHYSICS 62 RELATIVITY kzbin.info/aero/PLX2gX-ftPVXUHWgsWbVG3__1dC8nKMvEi&disable_polymer=true

[@thvyngvyen]

Thank you very much sir, I am sorry for spamming in the comment. I was not be able to comment earlier but I am not sure why it works now.

[@MichelvanBiezen]

KZbin filters comments automatically, depending on the wording and content.

[@amandakainz1482]

great instructions! This is really helping me!

[@naeemghafori5046]

but sir train B is not moving towards the left against train A why we took it minuse ???

[@MichelvanBiezen]

Let's say that person A and person B are not moving. How would you calculate how fast A moves relative to B with only the cars moving?

[@ashwina5472]

Two trains A and B of length 400 m each are moving on two parallel tracks with a uniform speed of 71 km h-1 in the same direction, with A ahead of B. The driver of B decides to overtake A and accelerates by 1 ms-1. If after 50 s, the guard of B just brushes past the driver of A, what was the original distance between them? sir how to solve this problem give some hints

[@MichelvanBiezen]

extra distance traveled by B during those 50 sec = (1/2) a t^2 = (1/2) * 1 * 50^2 = 1250 m

[@ashwina5472]

Michel van Biezen sir can we solve this problem by finding the distance travelled by A and by B separately and subtract it,to get the answer

[@MichelvanBiezen]

You can, but since they both start out traveling at the same speed, it is easier to ignore their initial speed.

[@ashwina5472]

thank you sir

[@marielle2213]

Sir, is a linear motion the same with one dimensional motion?

[@MichelvanBiezen]

Marielle, Yes. Linear motion and one-dimensional motion is considered the same

[@marielle2213]

thank you

[@davisjohn-d6h]

I am confused