Answer:
The train should be a 10 meters away before the professor falls
Explanation:
Calculation of the teacher's fall time:
[tex]y(t)=v_{o}t-1/2*g*t^{2}[/tex]
in this case Vo=0 and y=-5:
[tex]-5=-1/2*10*t^{2}[/tex]
[tex]t=1s[/tex]
Calculation how far away is the train when the professor falls:
The distance the train travel while the professor is falling:
[tex]d=v_{train}*t=10m/s*1s=10m[/tex]
So the train should be a 10 meters away before the professor falls