ATAR Notes: Forum
Archived Discussion => 2010 => Mid-year exams => Exam Discussion => Victoria => Physics => Topic started by: a.zirek on June 08, 2010, 10:29:22 pm
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For questions 15-17 I got ABB
What did you guys get?
My teachers been telling me it's AAA but I still stand by my result.
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ABB is correct.
Momentum is not lost as the spring compresses.
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ABB. Momentum is always conserved, during and throughout.
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yup, definatly ABB
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Its ABB
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These threads make me question the quality of the teachers in some schools =/
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ABB.
I was confused between whether to choose A and B for 16 and 17, because i was thinking that the two trolleys would lose speed temporarily. But then I saw the word "System" and that sealed it.
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Yeah, as if you're teacher is saying that ...
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I said AAC :/
Why was the last one B though?
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It said momentum not kinetic energy. I had C initally aswell.
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I know, but why is momentum conserved in the spring? Wouldn't you think that they would both slow down, therefore have a smaller momentum while the spring is being compressed?
I'm not saying that I'm right, I'm fairly sure that I'm wrong, this is just my reasoning.
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Because the conservation of momentum is derived off Newton's third law. F(A) = -F(B). As long as the objects exert equal and opposite action-reaction forces on each other, and these are the only forces acting on the objects (an isolated system) then momentum will be conserved.
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I know, but why is momentum conserved in the spring? Wouldn't you think that they would both slow down, therefore have a smaller momentum while the spring is being compressed?
I'm not saying that I'm right, I'm fairly sure that I'm wrong, this is just my reasoning.
sounds logical
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Momentum should be conserved no matter what in that kind of situation. So ABB
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Momentum should be conserved no matter what in that kind of situation. So ABB
i agree but wtf happens to the momentum whilst the spring compresses?
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I thought of it like this...
In an inelastic collision, we have Ek transferred to heat,sound energy and the total energy after the collision is less than the initial. BUT, the momentum is still the same.
Sooo.... if we were to have some of the energy momentarily transferred to the spring, wouldn't we still have the same momentum?
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Omg... momentum is ALWAYS conserved.
/facepalm
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Momentum should be conserved no matter what in that kind of situation. So ABB
i agree but wtf happens to the momentum whilst the spring compresses?
It was a frictionless table, so it's not as if the spring had to 'build up energy' in order to push the other block as it got scrunched up. It's the contrary, actually, as soon as the spring even bumps the second block, that second block goes flying away. So during the whole experiment, momentum was smoothly transferred, with a constant total amount.
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i got B,B,B - i just don't get y the teachers still think the answers are AAA
( ey and anil, btw the guys on itute think its A,B,B aswell. so i think maybe arif failed)
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It said momentum not kinetic energy. I had C initally aswell.
Oh bugger. Thought I had got full marks.
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Oh that sucks.
I just found out that I did got full marks. :)
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Oh that sucks.
I just found out that I did got full marks. :)
Well done!
Guess I learnt a valuable lesson - The question will not always be what you're expecting it to be.