What is the velocity of a snail moving toward the
door at 1 inch per hour?

the correct answer to the question is it has inertia.

explanation:

the splashing of water in the bottle can be explained in terms of inertia of motion.

from newton's first law of motion, we know that a body moving with uniform velocity along a straight line will keep on moving with the same velocity along that line unless and until it is compelled by some external unbalanced force. it is known as inertia of motion.

as per the question, the passenger is in the moving car. the open water bottle has the same velocity as that of passenger as he is holding the bottle.

when the car stops, the passenger will move in forward direction due to the inertia of motion. same also happens in case of water present in the bottle. the water splashed out as its inertia of motion is destroyed .