What is the average speed during acceleration?

[anglum]

Homework Statement

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.

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?

 

[Feldoh]

Homework Statement

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.

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?

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

 

[D H]

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.

Edited to add:
As you divide the interval into ever small chunks, the average of the speeds does approach the average speed. It is far easier to calculate the average speed as defined.