Answer
See the graph below.
Work Step by Step
The roof tail starts to fall from rest under the free-fall acceleration and then hits the water surface of the pool. After that, it moves down through the water at a constant velocity since the water viscosity of the water applies a friction force that opposes the weight of the roof tail and is just equal to it.
The two forces are having the same magnitude and opposite directions. Thus, in the water, the acceleration of the roof tail is zero.
See the graph below.
