# A and C collide with B inbetween; AB elastic, BC inelastic

#### haruspex

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both the equality of the masses and speeds of the two balls and the given that the glider is initially at rest are important considerations to the correct answer.
For the answer to the first part, yes, but that is not contentious.

Statements A and B are both correct in that they can be deduced from the given facts. You could take either of those statements, combined with the original facts, to deduce that the glider moves to the right. Therefore in order to answer the question of which of A and B, if either, is sufficient to deduce that the glider moves to the right you must not be allowed to combine those statements with the other original facts.

#### kuruman

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Statements A and B are both correct in that they can be deduced from the given facts. You could take either of those statements, combined with the original facts, to deduce that the glider moves to the right.
I agree so far.
Therefore in order to answer the question of which of A and B, if either, is sufficient to deduce that the glider moves to the right you must not be allowed to combine those statements with the other original facts.
Here is where we part company. I fail to see why this statement necessarily follows. If one "must not be allowed" to combine the statements with the other original facts in the context of choosing an answer, then why were the original facts given to begin with? I think that what necessarily follows is that we have a poorly constructed multiple choice question because it has two answers that can be correct if all the given facts are considered.

#### haruspex

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2018 Award
it has two answers that can be correct if all the given facts are considered.
That is why you must exclude them. The point of the question, I believe, is to distil that feature of the given facts that, by itself, leads to the result that the glider moves right.

"A and C collide with B inbetween; AB elastic, BC inelastic"

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