Finding the Radial Velocity Component of a Point P with Given Velocity Vector v

[matteo86bo]

Hi there,
I'm really ashamed of doing this stupid question but I really need help with this thing. And, even if it's simple, it's not homework.

I have a point P=(x,y,z) with velocity v=(vx,vy,vz)
how can I determine the radial component of the velocity?

My answer is that, $$v_r=vcos(\theta-\alpha)$$ where $$\theta,\alpha$$ are the angle between the x direction and the radial direction and atan(vx/vy).

Is this right?

 

[arildno]

Make the dot product between the unit vector $$\frac{1}{\sqrt{x^{2}+y^{2}+z^{2}}}(x,y,z)$$ and the velocity vector, and you have the radial component of the velocity.

Hmm..doesn't LateX work todaY?

 

[matteo86bo]

thanks arildno,
It was really easy! It's just that sometimes I get confused with this staff.