# Homework Help: Average velocity problem

1. Sep 5, 2012

### Violagirl

1. The problem statement, all variables and given/known data

A falling object moves so that its height x above the ground at time t is given by the following equation: x = 100 m - (4.9 s-2)t2. Find its average velocity from t = 0 t t = 2 s.

2. Relevant equations

Average velocity = Δx/Δt

3. The attempt at a solution

I was able to work it out to the point where I solved for x by plugging in the times given for 0 secs and 2 secs.

For t = 0:

x = 100 m - (4.9 s -2 * (0 s)2

= 100 m

For t = 2:

x = 100 m - (4.9 s -2 * (2 s)2

= 19.6 m

Solving for t2 in the equation, I get:

100 m/4.9 s-2 = t2

Final answer of 4.52 m s -2

For the average velocity equation (and t), I realize this does not work all that great as m will be cancelled in setting up the average velocity equation and am only left with seconds for time. I'm not sure what it is that I'm doing wrong in this problem. Thank you everyone for your help.

2. Sep 5, 2012

### PeterO

Average velocity is just (final position - initial position) divided by time interval.
You have successfully found the initial and final positions.
You just need the time interval.

How long was it from t = 0 to t = 2 ?

3. Sep 5, 2012

### Violagirl

Oh ok, got it! I guess I was just overthinking it, oops ...Thanks a lot!