Need help on making assumptions in maths

In my maths problem, there is a turtle race of 10m consisting of 4 turtles.

One of the questions is "In order to consider the race fair several assumptions need to be made". List these assumptions and the effects of these assumptions".

So far i have:

1) We assume all the turtles are the same weight, if one turtle was heavier it would give that turtle a disadvantage

2) We assume the turtles become tired when their speed changed

3) We assume the terrain is smooth, because if one turtle hit a rock it would slow it down and make the race unfair

What are some other assumptions that i could make? Could i use air resistance and friction as an assumption?