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## Homework Statement

(a) A particle has a displacement r1 = (35.0i + 12.0j + 14.0k) m at 29.0 s. At 53.0 s the ball has a displacement of r2 = (35.0i + 6.0j + 11.0k) m.

What is the average speed of the ball between 29.0 s and 53.0 s?

## The Attempt at a Solution

Having checked the answers, I already know that the

**average velocity**of the ball between 29.0 s and 53.0 s is:

[tex]0i-0.25j-0.125k[/tex].

The answers suggests that the

**average speed**of the ball is

**0.28 m/s**. How do I obtain this answer?

I got the average velocity using the formula [tex]v_{x, avg} = \frac{\Delta x}{\Delta t}[/tex] where x is the displacement. I think to find the average speed I must use [tex]v_{avg} = \frac{d}{\Delta t}[/tex] where d is the total distance traveled. But I don't understand why average velocity is in 3 components whereas the average speed is just a single number!