Suppose we were in a spaceship in free fall, where objects are weightl

Question

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.   1 
 1. It can be inferred from the passage that the two procedures described in the passage have which of the following in common?

A They have been applied in practice.
B They rely on the use of a device that measures tension.
C Their purpose is to determine an unknown mass.
D They can only be applied to small solid objects.
E They involve attraction between objects of similar mass.

2 
 2. According to the passage, the tension in the string mentioned in highlight text is analogous to which of the following aspects of a double-star system?

A The speed with which one star orbits the other
B The gravitational attraction between the stars
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

3 
 3. Which of the following best describes the relationship between the first and the second paragraph of the passage?

A The first paragraph provides an illustration useful for understanding a procedure described in the second paragraph.
B The first paragraph describes a hypothetical situation whose plausibility is tested in the second paragraph.
C The first paragraph evaluates the usefulness of a procedure whose application is described further in the second paragraph.
D The second paragraph provides evidence to support a claim made in the first paragraph.
E The second paragraph analyzes the practical implications of a methodology proposed in the first paragraph.

4 
 4. The author of the passage mentions observations regarding the period of a double-star system as being useful for determining

A 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
D the degree of gravitational attraction between the system’s stars
E the speed at which the star system moves through space

5 
 5. The primary purpose of the passage is to

A. analyze a natural phenomenon in terms of its behavior under special conditions
B. describe the steps by which a scientific measurement is carried out
C. point out the conditions under which a scientific procedure is most useful
D. contrast two different uses of a methodological approach in science
E. explain a method by which scientists determine an unknown quantity

RC00222-05.02

KarishmaB · Answer

"Contrast" means to show differences. 
The passage shows how the principle of the spring balance is used to measure the mass of stars. It does not contrast two different uses.

TheUltimateWinner · Answer

Hi  GMATNinja 
Thank you very much for the explanation.
In this question, the correct choice is A, but I picked the wrong choice (B).
In the passage, the word  suppose   means it is going to be  hypothetical situation . For that reason, I've chosen B for the word  hypothetical situation  in the answer choice B.

I've crossed out choice A because of the word  illustration . The word  illustration  is definitely connected with   example  , But the first para has no  example  at all, unfortunately. I can't figure out that whether any  illustration  in the first para?
Thanks__

TheUltimateWinner · Answer

Hi  BrightOutlookJenn 
Hope you're well. It is long time you're out of gmatclub-we missed you!
I've a query for this one. Could you help me, please? I'm seriously appreciating your help.

In this question, the correct choice is A, but I picked the wrong choice (B).
In the passage, the word  suppose   means it is going to be  hypothetical situation . For that reason, I've chosen B for the word  hypothetical situation  in the answer choice B.

I've crossed out choice A because of the word  illustration . The word  illustration  is definitely connected with   example  , But the first para has no  example  at all, unfortunately. I can't figure out that whether any  illustration  in the first para?
Thanks__

BrightOutlookJenn · Answer

Hi  TheUltimateWinner

Hey, thanks for the tag! Happy to be back.

You asked about the word  illustration , and indeed, we do have an illustration (specific description/example) given in the first paragraph. Here it is:

This whole description about how we could use a spring scale and swing it in a circle, and so on ... this is an  illustration .

Regarding answer choice B, it is incorrect because of the words "whose plausibility is tested." This would mean that the second paragraph attacks the believability or probability of the example, which is not at all what is going on in the second paragraph. If the author were  testing the plausibility  of the hypothetical in the first paragraph (the spaceship in free fall), we would need to see see something like, "But most people will never experience a spaceship in free fall, leading some researchers to question the wisdom of using such an unrealistic example."

The test writers caught you with the trap of "hypothetical" -> you matched it with "suppose", as you described, but you were not as critical about the rest of the words in the answer choice. Watch out! Test writers LOVE to begin answer choices with something correct and then screw it up later in the phrase. Always be sure to read  all the way to the end  of your preferred answer choice and make sure you can agree with every word.

Does that help? Let us know!

GMATNinja · Answer

Question 3, redux 
 
The words "hypothetical" and "illustration" are not mutually exclusive. The whole point of the first paragraph is to use everyday objects (springs, strings, etc) to explain a tricky concept. In other words, the author  illustrates  this concept using a simple example. Sure, the illustration is hypothetical -- but it's still an illustration.

Then, in the second paragraph, the author describes an "analogous procedure" that is used to measure the mass of stars. It's easier to understand this abstract procedure because of the nice illustration provided in the first paragraph.

(A) is looking good.

Here's (B):
 
The first paragraph does describe a hypothetical situation. But its plausibility isn't tested in the second paragraph -- the author never "tests" whether the example from the first paragraph is likely to be true. Instead, he/she just uses the example to explain the procedure described in the second paragraph.

(B) is out, and (A) is the correct answer to question 3.

KarishmaB · Answer

Responding to a pm:
 
What does the passage do?

Answer: It explains a method by which scientists determine an unknown quantity.

method - tension in the string
unknown quantity - mass of a star

Answer: It explains the method "tension in the string" by which scientists determine the masses of stars.

You can write your answer as with as much specific detail as you wish but both are correct.

For example: 
Question: What was he talking about?
Answer: He was telling a story.
or
Answer: He was telling the story of Alibaba.

Both are correct.

waytowharton · Answer

KarishmaB   GMATNinja   GMATNinjaTwo   Sajjad1994   bm2201 
I have doubt in option B and E.

5. The primary purpose of the passage is to

A. analyze a natural phenomenon in terms of its behavior under special conditions
B. describe the steps by which a scientific measurement is carried out
C. point out the conditions under which a scientific procedure is most useful
D. contrast two different uses of a methodological approach in science
E. explain a method by which scientists determine an unknown quantity

However, as per my reasoning I am finding option B better than E because option E states 'explain a method' while we discussed 2 methods(one in passage 1 and other in passage 2) in the passage and additionally option mentions scientists whereas in the passage astronomers measure. If we look the 2 para steps are mentioned to determine mass with various steps being observe time, measure distance, deduce gravitational force, and finally determine mass. Please explain why is option B wrong.

KarishmaB · Answer

I have taken this query here: https://gmatclub.com/forum/suppose-we-w ... l#p2544504 'Scientists' is a generic term used for people studying any kind of science so it is acceptable. The real difference lies in "describe the steps" and "explain a method". Describe the steps would be "first, tie the object to a spring... then swing it really fast ..." etc. That is not what the passage does. It tells you the method used to measure the masses. It explains you the concept and then how it is applicable to a star system. Hence (E) is better than (B). Note that we have discussed only one method. Tying to a string and whirling. We are applying that same method to the stars. There is an explanation of the method given to you and then how that method is applied to stars.

woohoo921 · Answer

KarishmaB Thank you for your helpful explanations, as always. For question "it can be inferred from the passage that the two procedures described in the passage have which of the following in common?" Choice B is incorrect because the hypothetical example mentioned in paragraph 1 uses a physical device whereas there is no physical device to measure tension in the second paragraph, correct? Both measure tension (paragraph 2 says "this attractive force, analogous to the tension in the string"), correct? Thank you again for all of your time and support / all your work on GMATCLUB

KarishmaB · Answer

Yes  woohoo921  
Option (B) is incorrect because only the principle is the same in both cases and the aim is the same (to measure the mass of an unknown quantity). But the second application of the principle does not use any device. 
... and you are most welcome!

abhishektyga · Answer

Why is C. the right answer for question 1? It asks what can be inferred but option C is directly mentioned in the first para. Please explain

KarishmaB · Answer

Between (B) and (E), the real difference lies in "describe the steps" and "explain a method".
Describe the steps would be "first, tie the object to a spring... then swing it really fast ..." etc. That is not what the passage does.
It tells you the method used to measure the masses. It explains you the concept and then how it is applicable to a star system. Hence (E) is better than (B).

RonTargetTestPrep · Answer

Notice the colored parts of B:

" Measurements " are  taken directly . Inferring or calculating a quantity from other figures is NOT "measuring" it.

Each paragraph focuses on a procedure that can be used to   infer   a particular mass  from other measurements  using principles of physical science.
These procedures take certain measurements as inputs, but are not measurements themselves.

Note further that the only "measurement" that IS, in fact, discussed in the second paragraph—"measuring the distance between stars"—is not explained in specific terms at all. Again contradicting B, there are no "steps" described for this measurement (about which I'm wondering myself! How do you 'measure' a distance between two things that are light-years away?)

E. explain a method by which scientists determine an unknown quantity

This is the right answer. It's true that two separate procedures are described (one per paragraph), each of which determines a different sort of unknown quantity—but, as confirmed near the beginning of the second paragraph, the point of the first procedure (first paragraph) is just to serve as the basis of an analogy by which the second procedure (the main focus) might be better understood.

GMAC's  short two-paragraph  passages are often—but not always!—structured this way, with the first paragraph serving mainly to set up the second in some way and therefore not figuring into a compact statement of 'main idea' or 'primary purpose'.

Diksha123456789 · Answer

For the primary purpose question, how is last option correct?
I says "method" but we have discussed two methods. Shouldn't B be the correct answer choice?

RonTargetTestPrep · Answer

The  PRIMARY purpose  is to explain the method described in the second paragraph—i.e., the technique that astronomers use to determine the mass of certain celestial objects.

The material in the first paragraph, about methods of weighing ordinary Earth objects using relatively simple machines and simple steps, is only there as an analogy to help the reader intuit the stuff in the second paragraph, which is the main point.

RonTargetTestPrep · Answer

Choice B says "  a   scientific measurement", which is still singular—so, if you don't like the singular nature of choice E, then you shouldn't like choice B (which uses a singular construction for precisely the same thing) either.

In any case, the real issue with choice B is the word "steps". A quick look through the second paragraph will quickly reveal that  steps  absolutely DO NOT appear there. 
In fact, the second paragraph pretty much contains everything EXCEPT the steps of the process! It mentions starting information, end goals, and (in generic broad-strokes terms) the overall nature of the mathematical/scientific process used to get from the start to the end. The  ACTUAL STEPS  that would get us from the start to the end, however, aren't there.

e.g.,

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 .

—> What is the ACTUAL PROCEDURE (step by step) for  measuring the distance between the stars ?

—> What are the ACTUAL CALCULATIONS (step by step) for  deducing the restraining force ? 
—> How about the ACTUAL CALCULATIONS for deriving  the masses  (= the end goals) from that result?

Absolutely nothing here to answer any of these three questions. No steps for anything.

RonTargetTestPrep · Answer

And one more thing you should absolutely keep in mind on problems like this:
• You can only have a "MAIN IDEA" in contrast to at least one SIDE POINT / PERIPHERAL IDEA / LOWER-PRIORITY IDEA.
• You can only have a "PRIMARY PURPOSE" as opposed to some sort of SECONDARY purpose.
etc etc

which means that...  the "main idea" or "primary purpose" or other answer to a BIG-PICTURE RC QUESTION  will absolutely  NEVER  mention EVERYTHING  that appears in the text.  
(In the same kind of way.. If a friend of yours goes to a talk, and then you ask this friend later "What did the speaker MAINLY talk about?"—If your friend actually spells out every single point that the speaker made the whole time, then you are not actually getting a valid response to the question that you asked.)

priyanshii26 · Answer

KarishmaB   Sajjad1994   Ninja 
in question 5, can you please let me know why option A is wrong?
I am confuse between a and e.

KarishmaB · Answer

Let me add one more thing here - when you say an option could be the answer, every word in the option needs to fit the passage.

A. analyze a natural phenomenon in terms of its behavior under special conditions

natural phenomenon - two stars in a double-star system circle one another
What special condition of the two star system are we talking about? None.

We are talking about how we can figure out their masses.

Sajjad1994 · Answer

Explanation

2. According to the passage, the tension in the string mentioned in highlight text is analogous to which of the following aspects of a double-star system?

Difficulty Level:   500

Explanation

The passage describes how the tension in the string, when an object is swung in a circle on a spring scale, is analogous to a certain aspect of a double-star system. Let's analyze each answer option to determine which aspect of the double-star system it corresponds to:

A.  This corresponds to the motion of one of the stars in the double-star system, but it is not analogous to the tension in the string mentioned in the passage.

B.  This is the correct answer. The passage explicitly states that the attractive force (gravitational attraction) between the stars in the double-star system is analogous to the tension in the string when an object is swung on a spring scale.

C.  This corresponds to the period of their motion, but it is not directly analogous to the tension in the string mentioned in the passage.

D.  This corresponds to the separation between the stars in the double-star system but is not analogous to the tension in the string.

E.  This corresponds to the combined mass of the stars, which is discussed in the passage but is not directly analogous to the tension in the string.

Answer: B

Suppose we were in a spaceship in free fall, where objects are weightl

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Suppose we were in a spaceship in free fall, where objects are weightl

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