# Average speed question

1. Sep 12, 2007

### anglum

1. The problem statement, all variables and given/known data
A car is moving at a constant speed of 13 m/s
when the driver presses down on the gas pedal
and accelerates for 11 s with an acceleration
of 1:4 m/s2.
What is the average speed of the car during
the period? Answer in units of m=s.

3. The attempt at a solution

using the formula distance = Vi t + 1/2 A t squared
i solve for distance and then just simply divide that by the 11 seconds?

Last edited: Sep 12, 2007
2. Sep 12, 2007

### Feldoh

Note sure what you mean by 1:4 m/s^2 -- But your solution looks right

3. Sep 12, 2007

### D H

Staff Emeritus
No. Average speed is defined as $\Delta d/\Delta t$, where $\Delta t$ is the duration of the time span and $\Delta d$ is the distance traveled during this span. If you average the speeds at arbitrary time points over the time interval you will get a different (and incorrect) answer.