Physical Science – MCAT: What Does a Passage Feel Like?

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If you haven’t heard already, the MCAT is hard. I struggled for a couple of weeks to come up with a succinct way to explain why it’s so hard, besides the reasons people might already have imagined. In vain I’ve kicked around a draft or two, those never made it past conception. And fruitless mulling now gives birth to this entry. Today’s post will focus on what an MCAT PS passage problem is like, the article is somewhat of a continuation of MCAT math entry I posted a while back. I wanted to show who the math and problem solving plays out during a passage. If you want more information about what’s on the current MCAT it’s best to keep up with the AAMC site, because the test is changing in 2015.

After you take enough practice test (you might even take all of them) you tend to pick up on the MCAT language, the MCAT feel. This is analogous to taking the same professor for the same serious, their testing style no matter how hard will eventually become familiar to you, no matter the subject. The AAMC tests are the only tests that actually measure your growth, the rest are assessments that try their best to emulate the MCAT. Some better do a better job than others. However, it can not be understated how hard the AAMC tries to make the one MCAT more or less equivalent to another MCAT (normalized for evolving prerequisites and recommended courses). I found that some MCAT exams seemed to be more “for me” than others, but again I can’t stress it enough, the MCAT is pretty consisted on what’s tested. It’s just that how you are asked will be different each time, sometimes it feels so different that it might take you a few weeks to understand why an answer is correct, even if you instinctively always get those questions correct. Everyone who sits for the real MCAT eventually falls victim to a cycle of realizing “Maybe, the answer was C, now that I think about it…”, viscous cycle.

It’s very difficult to talk about the MCAT PS passages, the subject of this post, without showing you the MCAT. But, with all the material being copyrighted (and with me avoiding arrests) we’ll have to compromise. I’ll make up an example of a passage, to give you a feel taste of what I mean without blowing a passage or me being put in padlocks.

I probably wouldn’t understand the passage entirely until the very end, or until I’ve answered all of the questions. This is very odd you might think, but this is because the MCAT is heuristic. In other words, the exam rewards test takers who can use their past experience to problem solve, learn as they go, and discovery a “best case” solution on the fly on new problems they’ve never seen before. MCAT passages are not as algorithmic as college course exams tended to be, that is you could probably give you a 20 page cheat sheet and a calculator on the MCAT and you’d likely either do the same or worse because you’d waste time on strategies that aren’t rewarded on the MCAT. The is the essence of the passages for the physical science section, in contrast the discrete questions reward people for their memory of MCAT fundamentals — the discrete questions should be the “free points” part of the test, but be aware most of the points will come from the passage as there’s more passage questions than discrete ones. Here’s the brief outline of the passage, I wrote a brief version, so you could skip over the superfluous explanation marked off by dotted lines:

Physical Science Universal Structure

1. Introduction to what is being measured or discussed.

2. Premises introduced.

3. Evidence presented possibly for or against the premises.

4. Conclusion of passage, typically ending abruptly, and flings you straight int the question stems*. It’s important that you don’t think of the question stems as just stand alone questions, they are entangled with the passage in some way. No matter how you feel, the passage is always right — unless it’s wrong, but in that case the MCAT is still right.

————–

Introduction

The test is great at shock and awe, assaulting your nerves from the first sentence — there’s a slight chance the sound of your heart beat will drown out all of your memory of the first sentence. But, the main goal is to keep a calm head, and jump straight into MCAT mode, and think “What is this passage about?”.

  • The beginning of the passage was the hardest part. It’s very easy to get three or four sentences in before I actually started focusing. You’ll likely go through all the 5 stages of grief while reading the passage, my best advice is to skip to acceptance before you start reading the first sentence.

2. Premises introduced and 3. Evidence presented possibly for or against the premises: Be an objective reader, note details, have confidence that you might understand the passage at some point in your life. 

  • The focus should be objective, you are on a fact finding mission and nothing else — all I need to care about is where I could find the explanation later if I needed it. There’s a good chance you’ll learn a lot about the passage by going through the questions, because the questions are sometimes more informative than the passage. So, don’t be sad if you feel like a college drop out after browsing through a passage, I don’t think they were expecting anyone to say “Ah, what an easy passage”.
  • Don’t bother thinking “Why the hell do I have to know about gauge pressure and deep under mining operation?” or “What does answering a passage about the effects of sulfur leeching into ground water in Indonesia have to do with becoming world’s best ___ doctor?”, it’s a waste of time. Just accept that it’s happening, you can eat a carton of Ben & Jerry’s later, don’t bother wasting test time or study time thinking about “why this passage?”. With that being said, on the real MCAT, my first thoughts were “Hell with this passage,, then I remembered it was the real test” haha. I buckled down from there, and never lapsed after that. Arguably, the most important task at the beginning of the passage is to first calm own, then to note what the subject of the passage is.
  • I would note where the explanations of the equations were in the passage or process I didn’t get. I wouldn’t actually care if I got it or not, I was confident at some point I might.
  • I would highlight numbers as I read them (this can be done on the computer with the real MCAT), maybe they would be important maybe the wouldn’t be. They often weren’t important, but knowing where they were made me feel better.

4. Conclusion of passage, typically ending abruptly.

  • I probably wouldn’t understand the passage entirely until the very end, or until I’ve answered all of the questions. This is very odd you might think, but this is because the MCAT is heuristicIn other words, the exam rewards test takers who can use their past experience to problem solve, learn as they go, and discover a “best case” solution on the fly on to new problems they’ve never seen before. MCAT passages are not as algorithmic as college course exams tended to be, that is you could probably give you a 20 page cheat sheet and a calculator on the MCAT and you’d likely either do the same or worse because you’d waste time on strategies that aren’t rewarded on the MCAT. The is the essence of the passages for the physical science section, in contrast the discrete questions reward people for their memory of MCAT fundamentals — the discrete questions should be the “free points” part of the test, but be aware most of the points will come from the passage as there’s more passage questions than discrete ones.

The best way to demonstrate what I mean is to give you a fake passage I just made up. I was inspired by some TV shows lately. The next paragraph will jump straight into the passage, brace for it, the MCAT will just throw you in with the lions after each passage:

Mock Physical Science Passage — This is what it feels like. But, before you begin I have to apologize for using the scientific notation system where 1×10^2  = 1E2, I was lazy and it looks better when typed without a math writing program. Good luck, and don’t lose focus!

Start

Schwarzchild radius (rs) is defined as the radius at which any body of mass (mo) must be compressed to create an event horizon, creating a black hole. The event horizon describes the boundary between rs, and the edge of spacetime where Netwonian physics still apply.

rs= 2GM/c^2

Object rs (meters)
Milky Way 2.08E15
Sun 2.95E3
Earth 8.87E-3

The first rigorous idea of a black hole came about from a solution to one of Einstein’s equations, and seen as nothing more than a mathematical “fluke” at the time. Another consequence of Einsteins theories was the melding of space with time, into the concept of unified space-time. Einstein had theorized that gravity was not so much a force as Newton had envisioned, but rather an effect of the warping of spacetime by mass. The more the mass the more the warping in space time. Black holes can contort space to such an extent that they can act like lens as described below.

theta = 4Gm/rc2 = 2rs/r

r = radius between observer and object creating gravitational lens

Now, we are aware that black holes are almost found ubiquitously throughout the universe, even our own galaxy has a super massive black hole at its center. On earth, it is theorized that the Large Hadron Collider (LHC) generates enough power to create microscopic black holes. Before the LHC was unveiled it was feared by some layman observers that, scientists would inadvertently create microscope black holes that could eventually engorge on Earth, devouring our entire solar system in what would be the largest scientific blunder in history. But, people need not fear, because the black holes would be so small and would evaporate almost instantly, all black holes are believed to evaporate at the rate described by t(ev) 

:

t(ev)= 5120 pi G^2*M^3/hc^4

G = universe gravitational constant = 6.67E-11m^3*kg^-1* s^-2

h = Planck’s Constant = 6.626E-34 J*s

c = speed of light = 2.99E8

Image

1. The final radius of a black hole is related to its mass, given Earth’s Schwartzchild’s radius what is Earths approximate weight?

A. 6E30 kg

B. 6,300,000 kg

C. 6E24 kg

D. 6E21 kg

2. Before ultimately colliding, black holes have been seen orbiting each other. If there are two black holes orbiting each other at distance r, and the radius is halved, how much does the force change between the two black holes? And what if the mass of one black hole is reduced to a 1/4th of it’s original value?

A. The force between black hole 1 and black hole two are equal and opposite. Because of the reduction in mass, the forces exerted between the two black holes would reduce by a 1/4th.

B. The force would be greater on the smaller black hole than the larger one.  Because of the reduction in mass,The forces exerted between the two black holes would increase by a 1/4th on the large black hole, and double on the large black hole.

C. The force would be four times as great on the smaller black hole.  Because of the reduction in mass, the forces exerted between the two black holes would reduce by a 1/4th.

D. The force would be half as much as before. The mass of the black holes no longer matter.

3. If a star is obscured slightly be the sun, and it is visible during a total solar eclipse on the Earth. If the light rays are bent towards Earth (towards the normal) what type of lens does gravity act as? Which wavelengths would be bent the most towards the normal?

A. Diverging lens, longer wave lengths like red would be bent harder.

B. Converging lens, shorter wave lengths will be bent harder.

C. Diverging lens, shorter wave lengths will be bent harder.

D. Converging lens, longer wave lengths will be bent harder.

4. Astronomers call black holes messy eaters, it is thought that perhaps half of the mass that is pulled into a black hole never makes it into the black hole itself due to various forms of turbulence. Eventually, this mass that never makes it can form an accretion disk. Some matter actually escapes the black hole, after being converted into pure energy is than remitted as gamma and X – rays. What if one solar mass (1.998E30 kg) is engulfed by a black hole, and 1 part per million of it’s mass is converted into pure energy how much energy would that be in joules ? (Updated!)

A. 2E133 joules

B. 2E 10 joules

C. 2E 34 joules

D. 2E41 joules

End

Get the idea? Scroll down for answers.

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Answer 1: C

Using the first equation, it’s just plug and chug. I’m going to estimate, because I’m lazy and it’s almost 2 AM. rs = 2Gm/c^2

I’ll just take care of 2G/c^2 at once, to make life easier = 2*6.626E-11/(3E8)^2 =

There’s no calculor on the MCAT so let’s say that is actually equal to

= 2*7E-11/(3E8)^2 = ~1.5E-27

Now,w it’s easy just take the equation rs = 2Gm/c^2, and isolate the m =

mass = 9E-3/1.5E-27 = ~6E24 kg 

Answer 2: A

I made this question easier, because on the MCAT there’s always a trick to it. And the question was too calculation heavy. Anyways, the forces are always opposite and equal for the MCAT, especially this is a cardinal rule for conservative forces. And mass is directly proportional to the force of gravity, as F = Gm1*m2/r^2. That second clause either helped you or hurt you. But, learn how to use all of the clauses of the questions to your advantage. Also notice that the clauses repeat every, the stem are repetitive — practice keeping track of the differences.

Answer 3: B

Converging lens, converging lens converge light. You didn’t have to read the passage to understand this, and the question stem did pretty much provide enough detail to figure it out without knowing about black holes as well. Next, you just ought to know shorter wavelengths get refracted more than longer wavelengths. If you couldn’t figure out the answer toe the first clause then you could of tried to make sense of the second clause first, or vice versa — that’s the lesson here.

Answer 4: D

Quick math really, just use E = mc^2, make Einstein proud. The hardest part, just like the real MCAT is remembering to do all the steps. If a solar mass is around 2E30 kg, 1 millionth of that would be 2E24 kg, this would be around the mass of Mars. Then E = mc^2 (expect a ridiculously huge number because usually we use this formula for small values), so that ends up being:

E = 2E30 kg *1E-6* (3E8)^2 m/s = ~18E41 = ~1.8E41 joules = ~2.0E41 joules. If you could harness that power to a 100 watt light bulb it would run for longer than the current age of the universe =x. In reality, the answers were so far apart that keeping track of the 2 and the 3 was pretty pointless. So, you could of done everything with 1E30 and (1E8)^2 and got an answer reasonable enough for the MCAT. If you see the ones place repeat in the answer, then the devils in the scientific notation. *This is a revision, a reader pointed out a typo, thank you!

The upside about MCAT passages is that you always walk away learning more than when you came in, whether you like it or not.

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3 thoughts on “Physical Science – MCAT: What Does a Passage Feel Like?

    sophie said:
    August 26, 2014 at 2:50 am

    For question 4, why is 2E30 used in the final calculation instead of 2E24? Thanks!

      doctororbust responded:
      August 26, 2014 at 3:24 am

      Typo 🙂

        doctororbust responded:
        August 26, 2014 at 3:27 am

        It should be around 2E41~

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