Comets do not give off their own light but reflect light : GMAT Critical Reasoning (CR)
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# Comets do not give off their own light but reflect light

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Comets do not give off their own light but reflect light [#permalink]

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20 Nov 2006, 11:59
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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: the greater a cometâ€™s mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halleyâ€™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 Halleyâ€™s comet is composed.
(B) Previous estimates of the mass of Halleyâ€™s comet which were base on its brightness were too low.
(C) The total amount of light reflected from Halleyâ€™s 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.
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20 Nov 2006, 12:05
Going for B
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20 Nov 2006, 12:20
Although we do not have choice E here i choose B also....
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20 Nov 2006, 13:22
Though I like B. I want to go for A.

Ak_idc where are you now? Can you please ellaborate about the option A?
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20 Nov 2006, 14:56
I am going with B also.

B is most supported here, especially with the following.

A satellite probe, however, has revealed that the material of which Halleyâ€™s comet is composed reflects 60 times less light per unit of mass than had been previously thought.
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20 Nov 2006, 17:28
agree with B.
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20 Nov 2006, 19:33
jyotsnasarabu 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: the greater a cometâ€™s mass, the more light that comet will reflect. A satellite probe, however, has revealed that the material of which Halleyâ€™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 Halleyâ€™s comet is composed.

No. We can't say that with certainty. It is however possible, if the method followed by scientists is accurate. But we are not sure of that accuracy. Not A

(B) Previous estimates of the mass of Halleyâ€™s comet which were base on its brightness were too low.

The argument says "the material of which Halleyâ€™s comet is composed reflects 60 times less light per unit of mass". So it has some thing to with material of the comet. Not mass. Also see the highlighted word "however" above. Usage of that word there indicates that the assumption "Scientists estimate the mass of comets by their brightness: the greater a cometâ€™s mass, the more light that comet will reflect" is not in tune with the findings of the satellite. Hence, I assume there is something wrong with the method of calculation used by scientists to calculate mass based on bright ness. Not B

(C) The total amount of light reflected from Halleyâ€™s comet is less than scientists had previously thought.

My answer. If the light per unit of mass comes down, and total mass is supposed to be constant, then total light reflected will come down. No?

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

We are not sure of this. We need another example or some more information.

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Last edited by ak_idc on 20 Nov 2006, 20:49, edited 2 times in total.
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20 Nov 2006, 20:28
Lovely question! Give me B!

premise 1: use reflected light to measure mass.
premise 2: more light, more mass
premise 3: Halley's material reflects less light per unit of mass than thought before.

The estimate of Halley's mass (say 100 KG) was based on a particular amount of light (say 1 unit) reflected. But now, that amount of light (1 unit) is less by 60 times than what should normally be reflected (60 * 1 = 60 units). So the mass of Halley's comet is actually much more (the mass that should be reflecting 60 units of light, but is actually reflecting only 1 unit because of some other reason).
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20 Nov 2006, 23:25
kripalkavi wrote:
Lovely question! Give me B!

premise 1: use reflected light to measure mass.
premise 2: more light, more mass
premise 3: Halley's material reflects less light per unit of mass than thought before.

The estimate of Halley's mass (say 100 KG) was based on a particular amount of light (say 1 unit) reflected. But now, that amount of light (1 unit) is less by 60 times than what should normally be reflected (60 * 1 = 60 units). So the mass of Halley's comet is actually much more (the mass that should be reflecting 60 units of light, but is actually reflecting only 1 unit because of some other reason).

u need a standin ovation
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20 Nov 2006, 23:42
kripalkavi wrote:
Lovely question! Give me B!

premise 1: use reflected light to measure mass.
premise 2: more light, more mass
premise 3: Halley's material reflects less light per unit of mass than thought before.

The estimate of Halley's mass (say 100 KG) was based on a particular amount of light (say 1 unit) reflected. But now, that amount of light (1 unit) is less by 60 times than what should normally be reflected (60 * 1 = 60 units). So the mass of Halley's comet is actually much more (the mass that should be reflecting 60 units of light, but is actually reflecting only 1 unit because of some other reason).

Here you are assuming that mass is same. From 60 units the light came down to 1 unit. So dont u think the total light has come down and is less now?

If so, is nt answer C is valid too?

I agree..Quantity of light is a vague thing to imagine..
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21 Nov 2006, 00:01
ak_idc wrote:
kripalkavi wrote:
Lovely question! Give me B!

premise 1: use reflected light to measure mass.
premise 2: more light, more mass
premise 3: Halley's material reflects less light per unit of mass than thought before.

The estimate of Halley's mass (say 100 KG) was based on a particular amount of light (say 1 unit) reflected. But now, that amount of light (1 unit) is less by 60 times than what should normally be reflected (60 * 1 = 60 units). So the mass of Halley's comet is actually much more (the mass that should be reflecting 60 units of light, but is actually reflecting only 1 unit because of some other reason).

Here you are assuming that mass is same. From 60 units the light came down to 1 unit. So dont u think the total light has come down and is less now?

If so, is nt answer C is valid too?

I agree..Quantity of light is a vague thing to imagine..

Thats just it! The quantity of light never reduced! The quantity of light remained the same. Something new about the material was discovered which said the material should be reflecting more light, but is actually not.
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21 Nov 2006, 02:04
i am also with ak_idc

The point is the mass is derived from the brightness.
But more the mass more is the light reflected,implies B
doesent apply.
Therefore theonly other possibility is for the total light reflected to be miscalculated.
I think so (C)
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21 Nov 2006, 02:12
kripalkavi wrote:
ak_idc wrote:
kripalkavi wrote:
Lovely question! Give me B!

premise 1: use reflected light to measure mass.
premise 2: more light, more mass
premise 3: Halley's material reflects less light per unit of mass than thought before.

The estimate of Halley's mass (say 100 KG) was based on a particular amount of light (say 1 unit) reflected. But now, that amount of light (1 unit) is less by 60 times than what should normally be reflected (60 * 1 = 60 units). So the mass of Halley's comet is actually much more (the mass that should be reflecting 60 units of light, but is actually reflecting only 1 unit because of some other reason).

Here you are assuming that mass is same. From 60 units the light came down to 1 unit. So dont u think the total light has come down and is less now?

If so, is nt answer C is valid too?

I agree..Quantity of light is a vague thing to imagine..

Thats just it! The quantity of light never reduced! The quantity of light remained the same. Something new about the material was discovered which said the material should be reflecting more light, but is actually not.

Now..I understand..

Scientists saw light first, and decided mass later. And not the other way round. And hence, they must have underestimated mass after seeing less light. The mistake was committed in terms of calculation of mass only, and not light. Agreed. B is the answer.
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21 Nov 2006, 12:36
The OA is B
21 Nov 2006, 12:36
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