Free Practice Question
RC · Reading Comprehension
sub-505
Short Passage - Science
Reading Passage
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.
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.
The author of the passage mentions observations regarding the period of a double-star system as being useful for determining
Answer Choices
Correct answer marked belowA
the distance between the two stars in the system
B
the time it takes for each star to rotate on its axis
C
the size of the orbit the system’s two stars occupy
the degree of gravitational attraction between the system’s stars
Correct
E
the speed at which the star system moves through space
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What it tests
Your ability to understand a passage, its structure, and what the author is really saying. At the sub-505 level, accuracy and speed both matter.
Common trap
Answering from memory or outside knowledge instead of strictly from the passage.
Details
Difficulty
sub-505
Type
RC
Category