# Average speed of a moving ball

1. Oct 9, 2012

### oldspice1212

Hey guys so I'm stuck and only have a couple tries left meaning I've lost quite some marks on this question already and I can't risk anymore so the question is...

A ball moves in a straight line (the x-axis). The graph in the figure (Figure 1) shows this ball's velocity as a function of time.
http://tinyurl.com/8fkkvrs (graph)

first question was: A) What are the ball's average velocity during the first 2.7 ?

I got 2.3 m/s for this

B) What are the ball's average speed during the first 2.7 ?

2.3 m/s as well but the next two I don't understand what I have to do...

C) Suppose that the ball moved in such a way that the graph segment after 2.0 was -3.0 instead of +3.0 . Find the ball's and average velocity during the first 2.7 in this case.

D) Suppose that the ball moved in such a way that the graph segment after 2.0 was -3.0 instead of +3.0 . Find the ball's average speed during the first 2.7 in this case.

2. Oct 9, 2012

### tiny-tim

hi oldspice1212!

speed is always positive (or zero): it's defined that way

in a car, speed is what it says on the speedometer

average speed is average reading of the speedometer​

velocity can be negative (in 2D or 3D, of course, it can be in any direction)

average velocity is total displacement over total time​

show us your next tries at C) and D) before you submit them!

3. Oct 9, 2012

### oldspice1212

For C I think it's (2+2-2.7)/3 to get the avg velocity which equals 0.43 but I got that wrong I'm not sure what i did wrong there.

4. Oct 9, 2012

### tiny-tim

it's not 2.7, and it's not 3

5. Oct 9, 2012

### oldspice1212

Err (2*2-3*0.7)/2.7?

6. Oct 9, 2012

yup!

7. Oct 9, 2012

### oldspice1212

Sweet and for D) would it be (2*2+3*0.7)/2.7 = 2.259..2.3

8. Oct 9, 2012

yes