Acceleration takes place the first 0-30 meters or to about 3-4 seconds from the start of a sprint. After approximately 30 meters acceleration turns into maximum velocity and top speed is hit.
In science, a hypothesis is an idea or explanation that you then test through study and experimentation. Outside science, a theory or guess can also be called a hypothesis. A hypothesis is something more than a wild guess but less than a well-established theory. In science, a hypothesis needs to go through a lot of testing before it gets labeled a theory. In the non-scientific world, the word is used a lot more loosely.
A null hypothesis is a hypothesis that says there is no statistical significance between the two variables in the hypothesis. It is the hypothesis that the researcher is trying to disprove. In the above example, Suzie's null hypothesis would be something like this: