2. 外语
  3. Suppose we were in a spaceship in free fall, where objects are weightless, and wanted to know a small solid object’s mass. We co

Suppose we were in a spaceship in free fall, where objects are weightless, and wanted to know a small solid object’s mass. We co

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问题 Suppose we were in a spaceship in free fall, where objects are weightless, and wanted to know a small solid object’s mass. We could not simply balance that object against another of known weight, as we would on Earth. The unknown mass could be determined, however, by placing the object on a spring scale and swinging the scale in a circle at the end of a string. The scale would measure the tension in the string, which would depend on both the speed of revolution and the mass of the object. The tension would be greater, the greater the mass or the greater the speed of revolution. From the measured tension and speed of whirling, we could determine the object’s mass.
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.
According to the passage, the tension in the string mentioned in lines 8-9 is analogous to which of the following aspects of a double-star system?
选项 A、The speed with which one star orbits the other
B、The gravitational attraction between the star s
C、The amount of time it takes for the stars to circle one another
D、The distance between the two stars
E、The combined mass of the two stars
答案B
解析 Supporting idea
The second paragraph states that an attractive force is analogous to the tension in the string. This attractive force is identified in the previous sentence as the gravitational force between the two stars in a double-star system.
A The second paragraph states that the speed with which the stars circle each other depends on the gravitational force between them, but it is that force that is analogous to the tension in the string.
B Correct. The second paragraph clearly identifies the gravitational force between the two stars as the attractive force that is analogous to the tension in the spring scale’s string.
C The amount of time it takes for the stars to circle one another is necessary for calculating the force that holds them together, but it is the force itself that is analogous to the string’s tension.
D The distance between the stars must be measured if the attraction between them is to be determined, but the attraction, not the distance, is analogous to the string’s tension.
E The combined mass of the two stars is what the procedure is designed to determine; it is analogous to the mass of the small solid object, as described in the first paragraph.
The correct answer is B.
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