Passage 1

Astronomers use an analogous procedure to “weigh” double-star systems. The speed with which the two stars in a double-star system circle one another depends on the gravitational force between them, which holds the system together. This attractive force, analogous to the tension in the string, is proportional to the stars’ combined mass, according to Newton’s law of gravitation. By observing the time required for the stars to circle each other (the period) and measuring the distance between them, we can deduce the restraining force, and hence the masses.

41.Based on the above passage, the following assumptions have been made:

1.The gravitational interactions are the overwhelmingly dominant forces dictating celestial orbital characteristics.

2.The observational data for the period and the distance between the stars can be acquired with a degree of precision.

Which of the assumptions given above are valid?

(a)1 only

(b)2 only

(c)Both 1 and 2

(d)Neither 1 nor 2

Question

Passage 1

Astronomers use an analogous procedure to &ldquo;weigh&rdquo; double-star systems. The speed with which the two stars in a double-star system circle one another depends on the gravitational force between them, which holds the system together. This attractive force, analogous to the tension in the string, is proportional to the stars&rsquo; combined mass, according to Newton&rsquo;s law of gravitation. By observing the time required for the stars to circle each other (the period) and measuring the distance between them, we can deduce the restraining force, and hence the masses.

41.Based on the above passage, the following assumptions have been made:

1.The gravitational interactions are the overwhelmingly dominant forces dictating celestial orbital characteristics.

2.The observational data for the period and the distance between the stars can be acquired with a degree of precision.

Which of the assumptions given above are valid?

(a)1 only

(b)2 only

(c)Both 1 and 2

(d)Neither 1 nor 2

ONLiNE UPSC · Accepted Answer

Statement 1 is correct: The passage states that the speed of circling depends on "the gravitational force between them, which holds the system together." For the subsequent deduction of masses based on period, distance, and this force to be valid, it must be assumed that this mutual gravitational force is the primary determinant of their motion. If other forces (e.g., from nearby stars, or other celestial bodies) were significant and not accounted for, the calculations of the masses would be inaccurate.

Statement 2 is correct: The passage states, "By observing the time required... (the period) and measuring the distance between them, we can deduce the restraining force, and hence the masses." This process of deduction relies on the input data (period and distance). If these fundamental observations cannot be made with sufficient accuracy, the derived values for force and mass would be unreliable or meaningless. Therefore, the feasibility of precise enough observation is a crucial prerequisite.

Astronomy

Double-star systems

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