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Comets do not give off

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Comets do not give off

by madhur_ahuja » Wed Jul 08, 2009 6:15 am
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 comet’s 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 Halley’s comet which were base on its brightness were too low.
(C) The total amount of light reflected from Halley’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.
(E) Scientists need more information before they can make a good estimate of the mass of Halley’s comet.
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by Sharma_Gaurav » Wed Jul 08, 2009 6:51 am
answer = C,

B - does not support,
A, D is not related to argument.
E is very broad and general and is not implied after reading argument. C is the best loking
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by cameronwu » Wed Jul 08, 2009 7:02 am
IMO the person who posted answer C is incorrect.

I think the answer should be B.

The premise of the argument is that scientists estimate mass of comets based on its brightness / reflection. Given that, scientists know how bright a comet is because that's the independent variable. Mass is the dependent variable. If you could express it as a function, it would be F(Brightness) = Mass.

Therefore, C is inaccurate because the scientists are not saying that it's any more or less bright. They're saying that the material reflects 60 times less light than they thought, which implies the mass of the comet is different than what they previously thought... it should be heavier because it requires more surface area / mass to reflect the same amount of light they measured, which is fixed.

If the light reflection is proportional to the mass calculation, this stimulus is essentially saying that the Comet is 60 heavier than what was originally estimated and thus (B).
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by madhur_ahuja » Wed Jul 08, 2009 8:00 am
cameronwu wrote:IMO the person who posted answer C is incorrect.

I think the answer should be B.

The premise of the argument is that scientists estimate mass of comets based on its brightness / reflection. Given that, scientists know how bright a comet is because that's the independent variable. Mass is the dependent variable. If you could express it as a function, it would be F(Brightness) = Mass.

Therefore, C is inaccurate because the scientists are not saying that it's any more or less bright. They're saying that the material reflects 60 times less light than they thought, which implies the mass of the comet is different than what they previously thought... it should be heavier because it requires more surface area / mass to reflect the same amount of light they measured, which is fixed.

If the light reflection is proportional to the mass calculation, this stimulus is essentially saying that the Comet is 60 heavier than what was originally estimated and thus (B).
I do not get this. If it is proportional, then it should be 60 times lighter, since the brightness is actually less now. Isnt it ?
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by raghavsarathy » Wed Jul 08, 2009 9:41 am
IMHO - C

B states that "the previous estimate of the mass of Haley's comet was very low"..

But this is not true as the main statement states that according to recent findings "haley's comet refelects lesser light than previously estimated". Previously they had estimated more light to be reflected due to greater mass of Haley's comet. Contradicted by B.
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by cameronwu » Wed Jul 08, 2009 10:12 am
raghavsarathy wrote:IMHO - C

B states that "the previous estimate of the mass of Haley's comet was very low"..

But this is not true as the main statement states that according to recent findings "haley's comet refelects lesser light than previously estimated". Previously they had estimated more light to be reflected due to greater mass of Haley's comet. Contradicted by B.
B - the stimulus does NOT say that the comet is "LESS BRIGHT" than previously estimated. It states that the material REFLECTS 60 TIMES LESS LIGHT per unit. It does NOT say that "THE COMET IS 60 TIMES LESS BRIGHT THAN ORIGINALLY THOUGHT." Whatever metric they used to judge the brightness is not a factor - The relationship that this stimulus is establishing is mass to brightness.

Imagine density. Let's say we have something, Substance A, that is 1 Kg/m^3. So for every Kilogram of mass it has, it occupies 1 cubic meter.

Now imagine something of less dense material, Substance B. Let's say it is .5 Kg / m^3. Because it has less density, it occupies two times more volume per the same mass as the other substance A.

This brightness concept is the same thing. Let's say that Haley's Comet is composed of material with Brightness index of 60, and assume that this is the standard by which all Comet's are evaluated. If the brightness is a certain fixed level, which I think you HAVE to assume (remember... it says the brightness is not 60 times less... it says the MATERIAL WHICH IT IS COMPOSED OF REFLECTS 60 times less than previously thought- they ARE NOT the same thing, i guarantee you). Now, if the brightness is the same, but the material that is reflecting is found to reflect 60 times less than what was previously imagined, it means the MASS HAS TO BE GREATER THAN PREVIOUSLY THOUGHT.

Think about it like this. Let's say 60(units of brightness/mass) x 5 (mass) = 300 brightness, and let this be the total brightness of haley's comet. This number doesn't change because it's an independent variable measure. Now, if we say that the 60 (brightness/mass) is actually discovered to light up a 1 (brightness/mass), then wouldn't the mass have to be 60 times greater to maintain the total units of brightness?

I realize my argument revolves around this assumption, but you are wrongly assuming that the question stimulus is saying the Comet is 60 times less bright than previously measured. It's just saying that the material which it's composed of reflects 60 times less light than the average comet, or 60 times less than whatever they usually base it on.
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by madhur_ahuja » Wed Jul 08, 2009 11:24 am
cameronwu wrote:
raghavsarathy wrote:IMHO - C

B states that "the previous estimate of the mass of Haley's comet was very low"..

But this is not true as the main statement states that according to recent findings "haley's comet refelects lesser light than previously estimated". Previously they had estimated more light to be reflected due to greater mass of Haley's comet. Contradicted by B.
B - the stimulus does NOT say that the comet is "LESS BRIGHT" than previously estimated. It states that the material REFLECTS 60 TIMES LESS LIGHT per unit. It does NOT say that "THE COMET IS 60 TIMES LESS BRIGHT THAN ORIGINALLY THOUGHT." Whatever metric they used to judge the brightness is not a factor - The relationship that this stimulus is establishing is mass to brightness.

Imagine density. Let's say we have something, Substance A, that is 1 Kg/m^3. So for every Kilogram of mass it has, it occupies 1 cubic meter.

Now imagine something of less dense material, Substance B. Let's say it is .5 Kg / m^3. Because it has less density, it occupies two times more volume per the same mass as the other substance A.

This brightness concept is the same thing. Let's say that Haley's Comet is composed of material with Brightness index of 60, and assume that this is the standard by which all Comet's are evaluated. If the brightness is a certain fixed level, which I think you HAVE to assume (remember... it says the brightness is not 60 times less... it says the MATERIAL WHICH IT IS COMPOSED OF REFLECTS 60 times less than previously thought- they ARE NOT the same thing, i guarantee you). Now, if the brightness is the same, but the material that is reflecting is found to reflect 60 times less than what was previously imagined, it means the MASS HAS TO BE GREATER THAN PREVIOUSLY THOUGHT.

Think about it like this. Let's say 60(units of brightness/mass) x 5 (mass) = 300 brightness, and let this be the total brightness of haley's comet. This number doesn't change because it's an independent variable measure. Now, if we say that the 60 (brightness/mass) is actually discovered to light up a 1 (brightness/mass), then wouldn't the mass have to be 60 times greater to maintain the total units of brightness?

I realize my argument revolves around this assumption, but you are wrongly assuming that the question stimulus is saying the Comet is 60 times less bright than previously measured. It's just saying that the material which it's composed of reflects 60 times less light than the average comet, or 60 times less than whatever they usually base it on.
Great Effort explaining this one. OA is B
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by james33 » Sun May 15, 2016 8:32 pm
I believe the answer should be C
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