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# Comets do not give off their own light but reflect light

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CEO
Joined: 15 Aug 2003
Posts: 3454
Comets do not give off their own light but reflect light [#permalink]

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17 Jul 2006, 21:31
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16. Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness by their brightness: the greater a comets mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halley's comet is composed reflects 60 times less light per unit of mass than had been previously thought.

The statements above, if true, give the most support to which one of the following?

(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley's comet is composed.

(B) Previous estimates of the mass of Halleys comet which were base on its brightness were too low.

(C) The total amount of light reflected from Halleys comet is less than scientists had previously thought.

(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.

(E) Scientists need more information before they can make a good estimate of the mass of Halley's comet.
VP
Joined: 25 Nov 2004
Posts: 1483
Re: Deja Vu CR: Halley's Comet [#permalink]

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17 Jul 2006, 21:53
go with B.

before:
mass = 100
brightness = 6000
brightness/unit of mass = 60

after:
mass = 6000
brightness = 6000
brightness/unit of mass = 1
brightness/unit of mass = 1

brightness of mass per un it is reduced because of the underestimations of mass previously.
VP
Joined: 07 Nov 2005
Posts: 1118
Location: India

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17 Jul 2006, 21:56
Picking D over C.
SVP
Joined: 30 Mar 2006
Posts: 1728

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17 Jul 2006, 22:00
Will go with B.

The amount of light a heavenly body reflects is proportional to its mass, but recent observations show that Haley's comet reflects less light than is proportional to its mass.
Hence previous predictions of its mass may be too low.
Senior Manager
Joined: 07 Mar 2006
Posts: 352

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17 Jul 2006, 22:02
Agree with MA's explanation.
CEO
Joined: 20 Nov 2005
Posts: 2894
Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008

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17 Jul 2006, 22:17
Should be B.

Scientists measured the brightness correctly but they measured the mass accoording to its brightness assuming that the mass wil lbe proportional to the brightness. But now they found that mass of comet reflects less light than they thought it means estimate of mass was incorrect.
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SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

Senior Manager
Joined: 31 May 2006
Posts: 368
Location: Phoenix AZ
Re: Deja Vu CR: Halley's Comet [#permalink]

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17 Jul 2006, 22:22
Praetorian wrote:
16. Comets do not give off their own light but reflect light from other sources, such as the Sun. Scientists estimate the mass of comets by their brightness by their brightness: the greater a comets mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halley's comet is composed reflects 60 times less light per unit of mass than had been previously thought.

The statements above, if true, give the most support to which one of the following?

(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley's comet is composed.

(B) Previous estimates of the mass of Halleys comet which were base on its brightness were too low.

(C) The total amount of light reflected from Halleys comet is less than scientists had previously thought.

(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.

(E) Scientists need more information before they can make a good estimate of the mass of Halley's comet.

B..
CEO
Joined: 15 Aug 2003
Posts: 3454

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18 Jul 2006, 08:48
Let me allow more time for others to participate. Will post the answer soon.
Senior Manager
Joined: 07 Jul 2005
Posts: 404
Location: Sunnyvale, CA

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18 Jul 2006, 09:16
(B) ..
Manager
Joined: 01 Jun 2006
Posts: 80

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18 Jul 2006, 10:20
I think it is E.

B uses the word "too", which may not be true.

E is a clear possibility due to the fact that the light levels are not sufficient to determine mass of the comet. And more info is needed.
Manager
Joined: 15 Nov 2005
Posts: 242
Location: Italy
Re: Deja Vu CR: Halley's Comet [#permalink]

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18 Jul 2006, 10:30
It took for me a lot of reasoning this one,...
B out estimates according to the passage previously where higher...
C is already included in the passage so is out

(A) Some comets are composed of material that reflects 60 times more light per unit of mass than the material of which Halley's comet is composed.

(D) The reflective properties of the material of which comets are composed vary considerably from comet to comet.

(E) Scientists need more information before they can make a good estimate of the mass of Halley's comet.

it seems now that among all the questions left the one that address all the passage is A
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Manager
Joined: 15 Nov 2005
Posts: 242
Location: Italy

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18 Jul 2006, 10:34
yes I agrre I have seen the reasoning is B....
_________________

â€œIf money is your hope for independence you will never have it. The only real security that a man will have in this world is a reserve of knowledge, experience, and ability.â€

CEO
Joined: 15 Aug 2003
Posts: 3454

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18 Jul 2006, 18:45
B is the correct answer. This was a difficult one.

Alternative explanations here:
http://www.gmatclub.com/phpbb/viewtopic ... leys+comet
18 Jul 2006, 18:45
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