• EMPOWERgmat Slider
    1 Hour Free
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    EMPOWERgmat Slider
  • Target Test Prep
    5-Day Free Trial
    5-day free, full-access trial TTP Quant

    Available with Beat the GMAT members only code

    MORE DETAILS
    Target Test Prep
  • Veritas Prep
    Free Veritas GMAT Class
    Experience Lesson 1 Live Free

    Available with Beat the GMAT members only code

    MORE DETAILS
    Veritas Prep
  • examPAL
    Most awarded test prep in the world
    Now free for 30 days

    Available with Beat the GMAT members only code

    MORE DETAILS
    examPAL
  • Economist Test Prep
    Free Trial & Practice Exam
    BEAT THE GMAT EXCLUSIVE

    Available with Beat the GMAT members only code

    MORE DETAILS
    Economist Test Prep
  • e-gmat Exclusive Offer
    Get 300+ Practice Questions
    25 Video lessons and 6 Webinars for FREE

    Available with Beat the GMAT members only code

    MORE DETAILS
    e-gmat Exclusive Offer
  • Magoosh
    Magoosh
    Study with Magoosh GMAT prep

    Available with Beat the GMAT members only code

    MORE DETAILS
    Magoosh
  • Kaplan Test Prep
    Free Practice Test & Review
    How would you score if you took the GMAT

    Available with Beat the GMAT members only code

    MORE DETAILS
    Kaplan Test Prep
  • Varsity Tutors
    Award-winning private GMAT tutoring
    Register now and save up to $200

    Available with Beat the GMAT members only code

    MORE DETAILS
    Varsity Tutors
  • PrepScholar GMAT
    5 Day FREE Trial
    Study Smarter, Not Harder

    Available with Beat the GMAT members only code

    MORE DETAILS
    PrepScholar GMAT

Exam Pack 2: RC ( Pendulum Clock)

This topic has 3 expert replies and 0 member replies
joealam1 Senior | Next Rank: 100 Posts Default Avatar
Joined
14 Aug 2016
Posted:
74 messages
Upvotes:
1
Target GMAT Score:
740
GMAT Score:
670

Exam Pack 2: RC ( Pendulum Clock)

Post Tue Dec 06, 2016 6:09 am
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

  • +1 Upvote Post
  • Quote
  • Flag

GMAT/MBA Expert

Post 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

  • +1 Upvote Post
  • Quote
  • Flag
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

Post 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.

_________________
Veritas Prep | GMAT Instructor

Veritas Prep Reviews
Save $100 off any live Veritas Prep GMAT Course

  • +1 Upvote Post
  • Quote
  • Flag
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

Post 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

  • +1 Upvote Post
  • Quote
  • Flag
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!

Best Conversation Starters

1 lheiannie07 108 topics
2 ardz24 67 topics
3 Roland2rule 63 topics
4 LUANDATO 50 topics
5 swerve 43 topics
See More Top Beat The GMAT Members...

Most Active Experts

1 image description GMATGuruNY

The Princeton Review Teacher

152 posts
2 image description Jeff@TargetTestPrep

Target Test Prep

106 posts
3 image description Rich.C@EMPOWERgma...

EMPOWERgmat

103 posts
4 image description Scott@TargetTestPrep

Target Test Prep

96 posts
5 image description Max@Math Revolution

Math Revolution

86 posts
See More Top Beat The GMAT Experts