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Mar 16, 2010
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Pre-Medical
i always get tripped up on these... type of questions on the aamc exams.

HOW are we supposed to look at these cuz sometimes they leave out things but that answer is still the best answer.... like they might leave out chemical to heat and then kinetic by saying chemical to kinetic and that might still be the answer.

for example there is a rocket question in the study guide aamc book:

chemical to kinetic to gravitational to heat

i chose, chemical to heat (cuz i thought chemical propelents to heated gas cuz thats what they said in the passage) to gravitational potential energy but they left out kinetic energy.

SO IS THE BEST ANSWER THE ONE THAT INCLUDES THE MOST ENERGY TRANSFERS WITHOUT SAYING ANYTHING WRONG?
 

notbobtrustme

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Jun 28, 2011
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i always get tripped up on these... type of questions on the aamc exams.

HOW are we supposed to look at these cuz sometimes they leave out things but that answer is still the best answer.... like they might leave out chemical to heat and then kinetic by saying chemical to kinetic and that might still be the answer.

for example there is a rocket question in the study guide aamc book:

chemical to kinetic to gravitational to heat

i chose, chemical to heat (cuz i thought chemical propelents to heated gas cuz thats what they said in the passage) to gravitational potential energy but they left out kinetic energy.

SO IS THE BEST ANSWER THE ONE THAT INCLUDES THE MOST ENERGY TRANSFERS WITHOUT SAYING ANYTHING WRONG?

Just think what happens when you turn on a rocket engine. You take chemical potential energy in the bonds of the propellant and combust them to produce heat and kinetic energy.
 
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Mar 16, 2010
131
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Pre-Medical
What was the question? You will have to elaborate a little.
Which of the following best describes teh energy conversion processes that occur during the flight of the rockt?

a) heat to kinetic energy
b) kinetic energy to gravitational energy and back to kinetic energy
c) chemical energy to kinetic energy and gravitational potetntial energy and then to heat
d) chemical energy to heat energy to gravitational potential energy

FROM PASSAGE:
the rocket was propelled up with fuel and then came down to earth via a parachute

CORRECT ANSWER: C

Now how do we go abotu choosing the right answer? DO WE CHOOSE THE ONE THAT INCLUDES the MOST WITHOUT IMPROPERLY INCORPORATING ANTHING. cuz clearly b makes sense but it doesnt have the MOST energy transfers and does not include everything and at the same time, c does not include the back from potential to kinetic and does not include the orignal chemical to heat AND THEN TO KINETIC
 

tn4596

7+ Year Member
Jul 23, 2011
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well the rocket is moving, so you know you will have kinetic energy somewhere. You just have to think about the situation with these questions...
 

karafox

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Jan 6, 2011
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Which of the following best describes teh energy conversion processes that occur during the flight of the rockt?

a) heat to kinetic energy
b) kinetic energy to gravitational energy and back to kinetic energy
c) chemical energy to kinetic energy and gravitational potetntial energy and then to heat
d) chemical energy to heat energy to gravitational potential energy

FROM PASSAGE:
the rocket was propelled up with fuel and then came down to earth via a parachute

CORRECT ANSWER: C

Now how do we go abotu choosing the right answer? DO WE CHOOSE THE ONE THAT INCLUDES the MOST WITHOUT IMPROPERLY INCORPORATING ANTHING. cuz clearly b makes sense but it doesnt have the MOST energy transfers and does not include everything and at the same time, c does not include the back from potential to kinetic and does not include the orignal chemical to heat AND THEN TO KINETIC
The passage gives you enough information to assume C.

1. Chemical energy: Chemical reactions from the fuel start the rocket
2. Mechanical energy:
(a) Chemical energy gets converted to kinetic energy (1/2mv^2), the rocket is moving faster and faster upward.
(b) As the rocket is slowing, kinetic energy decreases and gravitational potential energy increases. It doesn't slam back down to Earth. Think of when you're tossing a ball up and having it fall back into your hands. What happens to kinetic and potential energy?
3. Heat: the parachute is going against air resistance. The rocket is slowing down => friction => heat.
 
Feb 28, 2011
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He's not interested in getting into the nitty-gritty details -- he wants a quick, easy method. A quick easy method is process of elimination.

Step 1: You know the rocket is moving, so it has to have kinetic energy, so eliminate D.

Step 2: You know there is chemical energy because the rocket needs to convert fuel into energy. This eliminates A and B. You down to C -- pick it and move on.

For me, the heat energy is the toughest part of this problem because it was not apparent to me that when the rocket descends -- there's heat released -- but based on my method -- I did not even need to know that. On the MCAT -- precision and speed are important -- sometimes you just need to know 1 or 2 concepts to get the right answer without considering every possibility.
 

TheMightyBoosh

7+ Year Member
Feb 24, 2010
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He's not interested in getting into the nitty-gritty details -- he wants a quick, easy method. A quick easy method is process of elimination.

Step 1: You know the rocket is moving, so it has to have kinetic energy, so eliminate D.

Step 2: You know there is chemical energy because the rocket needs to convert fuel into energy. This eliminates A and B. You down to C -- pick it and move on.

For me, the heat energy is the toughest part of this problem because it was not apparent to me that when the rocket descends -- there's heat released -- but based on my method -- I did not even need to know that. On the MCAT -- precision and speed are important -- sometimes you just need to know 1 or 2 concepts to get the right answer without considering every possibility.
Excellent and really helpful explanation
 

whiteshadodw

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Dec 11, 2009
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sometimes you have to look at these questions in a different manner. you may not always like the correct answer choice, but it will be the best answer choice by far (and this is actually also what AAMC says, as much as i hate them).

we know a fuel is burned, propelling a rocket. in fact, if this question was a discrete, we could answer it still given the answer choices they gave us. combustion releases energy (it was originally stored as chemical potential) and this energy is converted to kinetic energy of the rocket (the rocket is propelled). if you simply made that connection you would see that C is the best answer. yeah, its not the perfect answer, but its the best answer there. the MCAT is all about speed as much as it is about accuracy, which combines to actually become mostly about efficiency. find the best answer as fast as possible.
 
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