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Register now and save up to $200 Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • Free Trial & Practice Exam BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code ## Exam Pack 2: RC ( Pendulum Clock) This topic has 3 expert replies and 0 member replies joealam1 Senior | Next Rank: 100 Posts Joined 14 Aug 2016 Posted: 74 messages Thanked: 1 times Target GMAT Score: 740 GMAT Score: 670 #### Exam Pack 2: RC ( Pendulum Clock) Tue Dec 06, 2016 6:09 am Elapsed Time: 00:00 • Lap #[LAPCOUNT] ([LAPTIME]) The ultimate pendulum clock, indeed the ultimate mechanical clock of any kind, was invented by a British engineer, William Shortt. The ﬁrst was installed in the Royal Observatory in Edinburgh in 1921. The Shortt clock had two pendulums, primary and secondary. The primary pendulum swung freely in a vacuum chamber. Its only job was to synchronize the swing of the secondary pendulum, which was housed in a neighboring cabinet and drove the time-indicating mechanism. Every 30 seconds the secondary pendulum sent an electrical signal to give a nudge to the primary pendulum. In return, via an elaborate electromechanical linkage, the primary pendulum ensured that the secondary pendulum never got out of step. Shortt clocks were standard provision in astronomical observatories of the 19205 and 19305, and are credited with keeping time to better than two milliseconds in a day. Many were on record as losing or gaining no more than one second in a year-a stability of one part in 30 million. The ﬁrst indications of seasonal variations in the earth's rotation were gleaned by the use of Shortt clocks. In 1984 Pierre Boucheron carried out a study of a Shortt clock which had survived in the basement of the United States Naval Observatory since 1932. After replacing the electromechanical linkage with modern optical sensing equipment, he measured the Shortt clock's rate against the observatory's atomic clocks for a month. He found that it was stable to 200 microseconds a day over this period, equivalent to two to three parts in a billion. What is more, the data also revealed that the clock was responding to the slight tidal distortion of the earth due to the gravitational pull of the moon and the sun. In addition to causing the familiar ocean tides, both the sun and the moon raise tides in the solid body of the earth. The effect is to raise and lower the surface of the earth by about 30 centimeters. Since the acceleration due to gravity depends on distance from the center of the earth, this slight tidal movement affects the period of swing of a pendulum. In each case the cycle of the tides caused the clock to gain or lose up to 140 microseconds. Question 1. The passage most strongly suggests that its author would agree with which of the following statements about clocks? A) Before 1921 no one had designed a clock that used electricity to aid in its timekeeping functions. B) Atomic clocks depend on the operation of mechanisms that were invented by William Shortt and ﬁrst used in the Shortt clock. C) No type of clock that keeps time more stably and accurately than a Shortt clock relies fundamentally on the operation of a pendulum. D) Subtle changes in the earth's rotation slightly reduce the accuracy of all clocks used in observatories after 1921. E) At least some mechanical clocks that do not have pendulums are almost identical to Shortt clocks in their mode of operation. OA:C How can we infere C + it is too extreme " No Clock" Question 2. According to the passage, the use of Shortt clocks led to the discovery that A) optical sensing equipment can be used effectively in time-keeping systems B) atomic clocks can be used in place of pendulum clocks in observatories C) tides occur in solid ground as well as in oceans D) the earth's rotation varies from one time of year to another E) pendulums can be synchronized with one another electronically OA:D Question 3. The passage most strongly suggests that the study described in the third paragraph would not have been possible in the absence of A) accurate information regarding the times at which high and low ocean tides occurred at various locations during 1984 B) comparative data regarding the use of Shortt clocks in observatories between 1921 and 1932 C) a non-Shortt clock that was known to keep time extremely precisely and reliably D) an Innovative electric-power source that was not available in the 1920s and 1930s E) optical data-transmission devices to communicate between the U.S. Naval Observatory and other research facilities OA:C Question 4. The passage most strongly suggests that which of the following is true of the chamber in which a Shortt clock's primary pendulum was housed? A) It contained elaborate mechanisms that were attached to, and moved by, the pendulum. B) It was ﬁrmly sealed during normal operation of the clock. C) It was at least partly transparent so as to allow for certain types of visual data output. D) It housed both the primary pendulum and another pendulum. E) It contained a transmitter that was activated at irregular intervals to send a signal to the secondary pendulum. OA:B Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums! ### GMAT/MBA Expert DavidG@VeritasPrep Legendary Member Joined 14 Jan 2015 Posted: 2301 messages Followed by: 115 members Thanked: 1069 times GMAT Score: 770 Mon Jan 09, 2017 5:34 pm Quote: The ultimate pendulum clock, indeed the ultimate mechanical clock of any kind, was invented by a British engineer, William Shortt. The ﬁrst was installed in the Royal Observatory in Edinburgh in 1921. The Shortt clock had two pendulums, primary and secondary. The primary pendulum swung freely in a vacuum chamber. Its only job was to synchronize the swing of the secondary pendulum, which was housed in a neighboring cabinet and drove the time-indicating mechanism. Every 30 seconds the secondary pendulum sent an electrical signal to give a nudge to the primary pendulum. In return, via an elaborate electromechanical linkage, the primary pendulum ensured that the secondary pendulum never got out of step. Shortt clocks were standard provision in astronomical observatories of the 19205 and 19305, and are credited with keeping time to better than two milliseconds in a day. Many were on record as losing or gaining no more than one second in a year-a stability of one part in 30 million. The ﬁrst indications of seasonal variations in the earth's rotation were gleaned by the use of Shortt clocks. In 1984 Pierre Boucheron carried out a study of a Shortt clock which had survived in the basement of the United States Naval Observatory since 1932. After replacing the electromechanical linkage with modern optical sensing equipment, he measured the Shortt clock's rate against the observatory's atomic clocks for a month. He found that it was stable to 200 microseconds a day over this period, equivalent to two to three parts in a billion. What is more, the data also revealed that the clock was responding to the slight tidal distortion of the earth due to the gravitational pull of the moon and the sun. In addition to causing the familiar ocean tides, both the sun and the moon raise tides in the solid body of the earth. The effect is to raise and lower the surface of the earth by about 30 centimeters. Since the acceleration due to gravity depends on distance from the center of the earth, this slight tidal movement affects the period of swing of a pendulum. In each case the cycle of the tides caused the clock to gain or lose up to 140 microseconds. Question 1. The passage most strongly suggests that its author would agree with which of the following statements about clocks? A) Before 1921 no one had designed a clock that used electricity to aid in its timekeeping functions. B) Atomic clocks depend on the operation of mechanisms that were invented by William Shortt and ﬁrst used in the Shortt clock. C) No type of clock that keeps time more stably and accurately than a Shortt clock relies fundamentally on the operation of a pendulum. D) Subtle changes in the earth's rotation slightly reduce the accuracy of all clocks used in observatories after 1921. E) At least some mechanical clocks that do not have pendulums are almost identical to Shortt clocks in their mode of operation. OA:C How can we infere C + it is too extreme " No Clock" In the second paragraph, we get the following quote about Shortt clocks: Many were on record as losing or gaining no more than one second in a year-a stability of one part in 30 million. So we know that these clocks, which rely on the operation of a pendulum, are extraordinarily accurate. In the next paragraph, in which the Shortt clocks are compared to atomic clocks, we see that the Shortt clocks are nearly as accurate as the atomic clocks, and we also get this: the data also revealed that the clock was responding to the slight tidal distortion of the earth due to the gravitational pull of the moon and the sun. So there's almost no difference in accuracy between the Shortt clocks and the atomic clocks (atomic clocks, presumably, being the standard for accuracy) and what difference exists is a function of tidal distortion. In the last paragraph, we get this line: this slight tidal movement affects the period of swing of a pendulum. Taken together we know that there's almost nothing more accurate than a Shortt clock; the Shortt clock only falls short of an atomic clock because the tide very slightly distorts its pendulum swing. Because any pendulum clock would suffer from this same distortion, it's reasonable to conclude that clock more accurate than a Shortt clock won't operate via a pendulum. So the answer is C _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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### GMAT/MBA Expert

DavidG@VeritasPrep Legendary Member
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Mon Jan 09, 2017 5:36 pm
Quote:
Question 2. According to the passage, the use of Shortt clocks
led to the discovery that

A) optical sensing equipment can be used effectively in
time-keeping systems

B) atomic clocks can be used in place of pendulum
clocks in observatories

C) tides occur in solid ground as well as in oceans

D) the earth's rotation varies from one time of year to another

E) pendulums can be synchronized with one another electronically
We can pull this one right from the last line of paragraph 2: The ﬁrst indications of seasonal variations in the earth's rotation were gleaned by the use of Shortt clocks.

D is a paraphrase of this idea.

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Save $100 off any live Veritas Prep GMAT Course Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now! ### GMAT/MBA Expert DavidG@VeritasPrep Legendary Member Joined 14 Jan 2015 Posted: 2301 messages Followed by: 115 members Thanked: 1069 times GMAT Score: 770 Mon Jan 09, 2017 5:38 pm Quote: Question 3. The passage most strongly suggests that the study described in the third paragraph would not have been possible in the absence of A) accurate information regarding the times at which high and low ocean tides occurred at various locations during 1984 B) comparative data regarding the use of Shortt clocks in observatories between 1921 and 1932 C) a non-Shortt clock that was known to keep time extremely precisely and reliably D) an Innovative electric-power source that was not available in the 1920s and 1930s E) optical data-transmission devices to communicate between the U.S. Naval Observatory and other research facilities The key line: he measured the Shortt clock's rate against the observatory's atomic clocks for a month So he's assessing the accuracy of the Shortt clock by comparing it to an accurate non-Shortt clock. The answer is C _________________ Veritas Prep | GMAT Instructor Veritas Prep Reviews Save$100 off any live Veritas Prep GMAT Course

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