Part a
Answer: 17.58 km/h

Total Distance =10 km
Total time =0.5689 h

Part b
Answer: 17.626 km/h

Total Distance =42.195 km
Total time =2.3939 h

We divide the thin rectangular sheet in small parts of height b and length dr. All these sheets are parallel to b. The infinitesimal moment of inertia of one of these small parts is

where

Now we find the moment of inertia by integrating from

to

The moment of inertia is

(from (-a/2) to

(a/2))
Because upward buoyant force is slightly higher than gravitation force for this particular object
Answer: The correct answer for the blank is -
C. closure.
Gestalt principle of closure describes how we perceive complete figures even when the information that form the figure is missing.
This is due the fact that our brain responds to the familiar patterns inspite of getting incomplete information.
For instance, in the given question, we are able to perceive an image of square in the center despite not having actual lines that form a square.
Thus, it represents principle of closure.