A runner of mass 50.1 kg starts from rest and accelerates with a constant acceleration of 1.1 m/s2 until she reaches a velocity of 6.5 m/s. She then continues running at this constant velocity. How long in seconds does the runner take to travel 104 m?

The given runner has a mass of 50.1 kg, and they begin their run starting from rest, and runs with a constant acceleration of 1.1 m/s².

This acceleration is maintained at a constant value, until the runner reaches a velocity of 6.5 m/s, and after reaching this velocity they maintain this at a constant. Thus this means after this mark the acceleration of the runner is zero.

The runner begins from rest, so the initial velocity is zero. A constant acceleration of 1.1 m/s² is maintained until a final velocity of 6.5 m/s is acheived.

Using kinematical equations of motion,

$$\begin{gathered} v=u+at \\ v is the final velocity at time t \\ u is the initial velocity \\ a is the acceleration \end{gathered}$$

So the time taken to reach 6.5 m/s is 

$$\begin{gathered} 6.5=0+1.1\times t \\ 1.1t=6.5 \\ t=\frac{6.5}{1.1} \\ t=5.909 s \end{gathered}$$