physics
posted by alyson .
i REALLY don't get this problem. PLEASE HELP!!!
the position of a runner during a 3 second time interval the runners position changes from x1 = 50m to x2 = 30.5m what was the runners average velocity?
find the average speed as well as the average velocity.

The velocity is both magnitude and direction. Let's consider velocity in the +x direction positive.
Then the average velocity would be
V = (x2x1)/t = (30.550)/3 = 6.5 m/s
which is negative.
The speed however is the magnitude of that vector or +6.5 m/s 
thanks a lot!!!!

If you have had the "unit vector" in your physics subject so far, then a unit vector in the x direction would be i, in the y direction j and in the z direction k
In this case the velocity is 6.5 in the x direction so you would write the velocity vector V as
V = 6.5 i 
or V = 6.5 i + 0 j + 0 k