# Couple of problems

1. Sep 8, 2013

### Alucard2487

1. The problem statement, all variables and given/known data
At a time 0.22 seconds after it has been hit by a tennis racket, a tennis ball is located at (6, 8, 0)  m, relative to an origin in one corner of a tennis court. At a time 0.26 seconds after being hit, the ball is located at (6.52, 8.16, 5.88)  m. Calculate the following results, and include correct units:

(b) What is the average speed of the tennis ball?

2. Relevant equations

3. The attempt at a solution

I had to calculate the average velocity. I got (13, 4, -3) m/s and I have the unit vector (.934, .287, -.215). i know that vavg = deltad/deltat. The problem is that the speed is a scalar and that confuses me.

2. Sep 8, 2013

### CWatters

Speed = Distance/Time.

You are given the time. Calculate the distance between the two points.

3. Sep 8, 2013

### consciousness

Given such a short time interval we can safely approximate the path of the ball to straight line by ignoring the effect of gravity. For a particle moving in a straight line which doesn't change its direction of motion the magnitude of the average velocity vector gives the average speed.