# Relative velocity of perpendicular vectors

1. Jan 16, 2010

### BogMonkey

Using this diagram as an example
http://img25.imageshack.us/img25/231/diagramig.jpg [Broken]
would I be right in assuming that the relative velocity of the boat with respect to the velocity of the current is the speed at which its moving away from say a stone floating down the river? In other words the resultant vector?

Last edited by a moderator: May 4, 2017
2. Jan 16, 2010

### Staff: Mentor

I think you mean:

Is the velocity of the boat with respect to the ground = the velocity of the boat with respect to the water + the velocity of the water with respect to the ground.

If that's what you mean, then yes.

3. Jan 16, 2010

### BogMonkey

It didn't make any sense what I was describing there did it. What I was trying to describe was something more like the relative velocity of the river with respect to someone jumping over the river but the resultant vector in that case would be the opposite direction. What I'm really wondering is whats the boats velocity with respect to the rivers current? Since the boats moving with the rivers current is relative velocity between the two vectors in this case meaningless? I can see the image of the boat crossing the river in my head its just the idea of relative velocity that has me confused. I suppose in this case its no different than someone canoeing across a frozen river meaning the rivers velocity can be neglected.

4. Jan 16, 2010

### Staff: Mentor

You mean the boat's velocity with respect to the water? What data are you given? You gave the boat's velocity (in the y-direction). What was that respect to? The ground? Use the formula I gave--in words--in my last post.