Relative velocity in Physics (1 Viewer)

[khorne]

Hey all

I just have a small question to ask:

When finding relative velocity there are two types of questions, right?

The velocity of Object A relative to B, which I believe is V(ab) = Va - Vb

And the other one is finding the relative velocity with respect to the ground when an object is in a medium, which is given by V(object,ground) = Velocity(medium current, ground) + Velocity(Object, medium current), right?

For example: If a plane is traveling 200m/s south, and hit by a wind of 50m/s coming from the east, the velocity of the plane relative to the ground would be

V(pg) = V(wg) + V(pw) = 50 m/s west + 200m/s south

Could anyone just confirm this?

Thanks a lot

 

[Omium]

Hey all

I just have a small question to ask:

When finding relative velocity there are two types of questions, right?

The velocity of Object A relative to B, which I believe is V(ab) = Va - Vb

And the other one is finding the relative velocity with respect to the ground when an object is in a medium, which is given by V(object,ground) = Velocity(medium current, ground) + Velocity(Object, medium current), right?

For example: If a plane is traveling 200m/s south, and hit by a wind of 50m/s coming from the east, the velocity of the plane relative to the ground would be

V(pg) = V(wg) + V(pw) = 50 m/s west + 200m/s south

Could anyone just confirm this?

Thanks a lot

Frames of reference made this topic a lot easier for me.

As a second year physicist, this is my most hated topic.

 

[khorne]

Just a few practice questions I want to check with you guys.

A boat sails at 8 ms-1 due north. There is a current of 15 ms-1, flowing from the west.

(a) What is the magnitude and direction of the velocity of the boat relative to the water?

Well, can't I assume the boat sails 8m/s N, as the boats velocity has to be relative to something, and in this case, we can take water as the frame of reference?

Or do we say that Vbw = Vb - Vw

(b) What is the magnitude and direction of the velocity of the boat relative to the ground?

V(bg) = V(bw) + V(wg)

Therefore V(bg) = 8m/s N + 15m/s E

Right?

 

[smp211]

I can very vaguely remember doing this but I will give my opinion.

With a), by saying the boat is 8ms^-1 due north, then i think we can take that as relative to the Earth.

if the current of water is said to be flowing from the west, then that is relative to the earth.

Vbe=8 north
Vwe=15 west

therefore... Vbw = vector sum 8 north + 15 west

simple pythagoris triangle...

we get 17 ms^-1 NorthWest

the boat relative to the earth must be 8 north....

as i said this is just me using logic since i cant remember how i used to do it, so i could be way off the mark, lol

 

[khorne]

With a), by saying the boat is 8ms^-1 due north, then i think we can take that as relative to the Earth.

if the current of water is said to be flowing from the west, then that is relative to the earth.

Vbe=8 north
Vwe=15 west

therefore... Vbw = vector sum 8 north + 15 west

Thank you for your insight, considering the question that does sound right.