Final answer:
In physics, assuming constant velocity (zero acceleration) simplifies equations describing motion, allowing easy computation of average velocity and confirming that growth rate of velocity is zero.
Step-by-step explanation:
When assuming that velocity is constant, as suggested by Irving Fisher, the growth rate of velocity is indeed zero. This concept is central to classical mechanics, specifically when dealing with constant acceleration.
A situation where velocity is constant implies that there is no acceleration, as acceleration is defined as the rate of change of velocity.
For motion at constant acceleration, which in our case is zero (a = 0), the formula V = Vo + at simplifies because the product of 'a' (acceleration) and 't' (time) will be zero, leaving us with a final velocity that is equal to the initial velocity ('Vo'). It also allows us to calculate the average velocity as simply the mean of the initial and final velocities.
If these are constant over time, the average will be the same as the initial and final velocities directly.
Therefore, if we observe a scenario where a train returns to its starting point without changing its velocity, we can conclude that its average velocity is zero, as its displacement is zero (xf = xo). Similarly, for a gazelle moving at a constant velocity, we can directly use the displacement over time to determine its velocity, given by the equation x = xo + vt.