The purpose of mechanics is to describe how bodies change their positi

The purpose of mechanics is to describe how bodies change their position in space with time. I should load my conscience with grave sins against the sacred spirit of lucidity were I to formulate the aims of mechanics in this way, without serious reflection and detailed explanations. Let us proceed to disclose these sins.

It is not clear what is to be understood here by “position” and “space.” I stand at the window of a railway carriage which is travelling uniformly, and drop a stone on the embankment, without throwing it. Then, disregarding the influence of the air resistance, I see the stone descend in a straight line. A pedestrian who observes the misdeed from the footpath notices that the stone falls to earth in a parabolic curve. I now ask: Do the “positions” traversed by the stone lie “in reality” on a straight line or on a parabola? Moreover, what is meant here by motion “in space”? From the considerations of the previous section, the answer is self-evident. In the first place we entirely shun the vague word “space,” of which, we must honestly acknowledge, we cannot form the slightest conception, and we replace it by “motion relative to a practically rigid body of reference.” The positions relative to the body of reference (railway carriage or embankment) have already been defined in detail in the preceding section. If instead of “body of reference” we insert “system of co-ordinates,” which is a useful idea for mathematical description, we are in a position to say: The stone traverses a straight line relative to a system of co-ordinates rigidly attached to the carriage, but relative to a system of co ordinates rigidly attached to the ground (embankment) it describes a parabola. With the aid of this example it is clearly seen that there is no such thing as an independently existing trajectory, but only a trajectory relative to a particular body of reference.

1. What can be inferred about the author from the first paragraph of this passage?

(A) The author agrees with the definition of a term as mentioned in the first line of the passage.
(B) The author wants to reflect on the definition of a term as mentioned in the first line of the passage.
(C) The author believes that concepts such as ‘space’ cannot be defined in absolute terms.
(D) The author does not completely agree with the definition of a term as mentioned in the first line of the passage.
(E) The author is a Physics expert.

2. If a stone were to be dropped—on a platform 20 feet below—from the window of a moving vehicle, which of the following must be true, according to the information in the passage?

(A) To a person sitting in the vehicle, the stone would appear to fall in the shape of a parabola.
(B) To a person sitting in another vehicle 500 metres behind, the stone would appear to fall in a straight line.
(C) To a person standing on the platform the stone would appear to fall in a straight line.
(D) To a person standing on the platform the stone would appear to fall either in a straight line or in the shape of a parabola.
(E) To a person standing on the platform the stone would appear to fall in the shape of a parabola.

3. The passage implies that scientists should refrain from doing which of the following?

(A) Coming up with theoretical definitions without judging the practical veracity of the same.
(B) Considering concepts in the field of Physics in absolute terms.
(C) Using vague terms while defining a concept.
(D) Relying on historical sources when trying to define a term.
(E) Attempting to define terms from the realm of Physics in the relative sense rather than in absolute terms.