Physics Lesson: Relative Velocity Part 2 Kinematics High School Tutorial

[cool12threeman]

Hi, do you have videos which solve swimmer problems like these but they involve scalene triangles not right triangles? If you could post them, it would be greatly appreciated.

[NardiNardi81]

at 4:45 should it be Vr= 4.47 s or Vr = 4.47 m/s ?

[YellowBananaaaa]

In the last video, you said that the swimmer's velocity relative to the water is what you actually use to calculate the time because the velocity of the current doesn't effect it. Why is it that in this video you use the resultant velocity (water+swimmer(relative to water)) to calculate the time in this video? Thanks for your reply in advance, great video btw.

[PhysicsEH]

@YellowBananaaaa I just found your question in my spam box. You don't have to use the resultant, what you do is use whatever component is parrallel with the displacement you're given. In swimmer questions you usually know the diplacement across the river so you match the displ. with the velocity component in that direction. In this question the resultant is in line with the displacement given. In that last video the swimmers velocity is in line (parallel) with the displ so I used that.

[siasorat]

isn't that north of east? cause you find the thetha and it should be north of east east of north would be the other way around 90-42?

[PhysicsEH]

@siasorat Hi. You can describe the direction using 2 different methods. One is to call it [E 42 N] which means point to the east and then move 42 toward the north. I think this method is the easiest but some teachers use the seocnd method. The second method writes it [42 north of east] which means go 42 degrees toward the north from the east. I find this method of naming more comfusing. I think you use this method and so my answer looks wrong to you. I hope this helps.

[ello1234567]

HOW THE HECK DID U DO A SQUARE ROOT IN YOUR HEAD!!!

[PhysicsEH]

@ello1234567 I'll tell you a little secret. The calculation answers are on the board just out of view of the camera. I can see the solution when I face the chalk board. Don't tell my students, they think I have a special power.

[someone20ify]

@PhysicsEH hahahah.....sir, ur not only smart, u r funny too!!!!

[ReddAlertt]

it's not loud enough.

[PhysicsEH]

@ReddAlertt Hi. The more we do this the better we get at having the sound a bit louder. We will keep trying to get it better. I hope you still found it usefull.

[TheCelltick]

thank you this just saved me from getting a C for the marking period :)

[PhysicsEH]

@TheCelltick Glad to help!

[072968688pk]

YOUR MY HERO

[PhysicsEH]

@072968688pk Wow. Thanks for the great compliment. Glad to help.

[AncientGearBeast]

@PhysicsEH

why didn't u do Vr^2= vs^2+Vw^2 square root?

[PhysicsEH]

@AncientGearBeast I should have made it more clear in the video that in this example Vr is not the hypotenuse. Pythagorean theorem has the hyp^2 = side^2 + other side^2. In this case one side is Vr, one side is Vw and the hypotenuse is Vs so the formual ends up being Vs^2 = Vr^2 + Vw^2. I hope this helps.

[PhysicsEH]

@AncientGearBeast I should have made it more clear in the video that in this example Vr is not the hypotenuse. Pythagorean theorem has the hyp^2 = side^2 + other side^2. In this case one side is Vr, one side is Vw and the hypotenuse is Vs so the formual ends up being Vs^2 = Vr^2 + Vw^2. I hope this helps.

[brucerd1]

I lack common sense...

I figured since Vr= Vs + Vw, then Vs= Vr - Vw, and then I did some vector subtraction. Anyway your video was really helpful especially the bit about the time being the same....

[GhuneDhoraGuitar]

thanks sir, big time life saver.