You can use the acceleration values from the accelerometer to measure the velocity. There is really good paper (Implementing Positioning Algorithms Using Accelerometers) which explains the errors you get from the accelerometer and the techniques to get the velocity and position from the acceleration values. To get the time the vehicle takes to accelerate from 0 to 100 km/h you have to measure the time until you reached a certain velocity.
The main steps you have to take to get the velocity from the acceleration values are
- get the acceleration values
- integrate over the values to get the velocity
Some hint:
velocity[i] = (acceleration[i] + acceleration[i-1])/2 * interval + velocity[i-1]
interval is the time between acceleration[i] and acceleration[i-1] which is related to the update frequency of the accelerometer.
To increase accuracy you have to filter the acceleration values in the forehand.
PS: I've implemented such an algorithm on an iPhone 3GS and it worked pretty good. The accelerometer let's you measure distances of 30 cm with an error of approximately 1 cm. I didn't tested longer distances yet.
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