Nextstep 2 Physics

Question 1

A climber using bottled oxygen accidentally drops the oxygen bottle from an altitude of 4500 m. If the bottle fell straight down this entire distance, what is the velocity of the 3-kg bottle just prior to impact at sea level? (Note: ignore air resistance)

Answer 1

300 m/s

Question 2

The hemoglobin (Hb) dissociation curve at high altitude has a distinct shape from that at atmospheric pressure. Which of the following best explains this shape?

Answer 2

igmoidal shape of the curve implies that as each oxygen molecule binds to Hb, the affinity of Hb for oxygen goes up. Homotropic regulation is when a molecule serves as a substrate for its target enzyme, as well as a regulatory molecule of the enzyme’s activity. O2 is a homotropic allosteric modulator of hemoglobin. The four subunits of hemoglobin actually bind to oxygen cooperatively, meaning the binding of oxygen to one of the four subunits will increase the likelihood that the remaining sites will bind with oxygen as wel

Question 3

Fluid pressure changes with depth are assumed to be linear. Which statement best explains why this does not hold true for atmospheric pressure

Answer 3

B is correct. Hydrostatic pressure for liquids is linear because as depth changes, the density of the liquid remains constant. Gases, however, have densities that change according to the forces applied to them. Gases are compressible, while liquids and solids are not.

Question 4

Which of the following most closely approximates the pKa of phenolphthalein?

Answer 4

D is correct. Indicators function in acid-base titrations to identify, via color change or a similar mechanism, that an expected pH, and thus the titration endpoint, has been reached. In order to function in this way, an indicator must undergo a color change near the desired pH. This typically occurs because of a reversible change in the protonation state of the indicator. It is desirable then that the pKa of a chosen indicator be within ±1 unit of the target pH. For the titrations performed in the study of acetic acid, a weak acid, and sodium hydroxide, a strong base, the endpoint of the titration will occur at a pH greater than 7. Of the possible pKa values given as answer choices, only D could function well as an indicator for a pH in this range.

Question 5

asparagine one letter amino acid?

Answer 5

N

Question 6

a positive control will help?

Answer 6

A is correct. A positive control is a control group that is not exposed to the experimental treatment but that is exposed to some other treatment that is known to produce the expected effect. The scientists wished to test the effect of the analogs on enzyme activity. Using a known inhibitor is an example of comparing the expected effects of this inhibitor to those of the analog treatment. Thus, it is a positive control.

Question 7

Which of the following phase changes are exothermic processes?

I. Liquid to gas

II. Liquid to solid

III. Gas to solid

Answer 7

D is correct. This question tests your understanding of reaction enthalpies. Reactions that proceed from solid to liquid to gas are endothermic reactions, since gases have more heat energy than liquids and liquids have more heat energy than solids. On the other hand, reactions that proceed from gas to liquid to solid release heat, making them exothermic reactions. Thus, II and III are both exothermic reactions, while I is an endothermic reaction.

Question 8

Pentane is a straight-chain hydrocarbon with the molecular formula C5H12. How many additional structural isomers can be constructed using this molecular formula?

Answer 8

2

Question 9

An object with a mass of 10 kg is rolled down a frictionless ramp from a height of 3 meters. If a factory worker at the bottom of the ramp slows the object until it comes to a stop, how much work must the factory worker have done? (Assume g = 10 m/s2.)

Answer 9

300J

Work is measured in Joules

Question 10

If the bicep exercises last 5 minutes, what is the total work performed by the patient’s muscle?

The passage says 50W

Answer 10

Power = work / time. Thus, work = power x time. Work = 50 W x 5 min = 50 J/s x 300 s = 15,000 J. This is equivalent to 15 kJ.

Question 11

What is the wavelength of the photons emitted by the 145Pm-m? (Note: 1 eV = 1.6 x 10-19 J)

Answer 11

D is correct. The energy of the photon is given as 300 keV. This will need to be converted to joules using the equation 1 eV = 1.6 x 10-19 J. The energy of a photon is related to its wavelength via the equation E = hc/λ, where h is Planck’s constant (6.62 x 10-34 J•s) and c is the speed of light (3 x 108 m/s). Thus,

λ = hc/E

Solving for λ, we get:

λ = [(6.62 x 10-34 J*s)(3 x 108 m/s)] / [(300 x 103 eV)(1.6 x 10-19)]

λ = 4.1 x 10-12 m

Question 12

Which of the following charged particles will be attracted to the particle emitted during the decay of 145Nd?

Answer 12

Coulomb’s law states that the force between two charged particles is attractive when the charges are opposite and repulsive when the charges are the same. Thus, if the emitted particle is negatively charged, then the particle attracted to it must be positive, like a positron. A positron is the same size and magnitude of the charge as an electron, but has a positive charge.

Question 13

An anti-neutrino carries?

Answer 13

NO CHARGE

Question 14

In the electron transport chain, which of the following is the component that is reduced but never oxidized?

Answer 14

This question is testing your knowledge of the electron transport chain. Almost all elements in the chain are at some point reduced and oxidized. This is the driving force behind the electron transport chain. However, at the end of the chain, oxygen is reduced to form H2O, which is the end fate of the electrons in the chain.

Question 15

In which of the following molecules does the carboxylic acid functional group have the highest Ka?

Answer 15

A higher Ka is associated with stronger acidity. Adding electron-withdrawing functional groups (like fluorine atoms) provides inductive stabilization of the conjugate base. This stabilization increases the acidity of the original compound. Inductive effects increase if the electron-withdrawing groups are closer to the acid and if more of them are present. Therefore, choice A is the most acidic.

Question 16

In oxidative phosphorylation, what is the final step?

Answer 16

This question is testing your knowledge of oxidative phosphorylation. The end purpose of oxidative phosphorylation is to phosphorylate ADP into ATP. We should know for the MCAT that the very final step is ATP synthase allowing protons to move down the electrochemical gradient while forming ATP.

Question 17

A 50-kg child is riding on a playground merry-go-round. If the radius of the circular path of the merry-go-round is 5.0 m and the frequency is 0.1 hertz, what is the force required to keep the child on the ride?

Answer 17

B is correct. If the frequency of the merry-go-round is 0.1 Hz, then the period is 10 s. We can calculate the speed of the merry-go-round from V = 2πr/T = 2(3.14)(5.0 m)/(10 s) = 3.14 m/s. Using this in the centripetal force equation:

Fc = mv2/r = (50 kg)(3.14 m/s)2/(5.0 m)

Approximate the square of the speed at 10 m2/s2.

Fc = (50)(10)/(5) = 100 N

Question 18

glycine is achiral because?

Answer 18

A is correct. The key word in the stem of the question is “achiral,” which means “not chiral.” The amino acids with side chains other than hydrogen are all chiral, because they have four different substituents attached to the α-carbon. The only amino acid that is achiral is glycine, because its side chain is a hydrogen atom. As a result, glycine does not have four different groups attached to the α-carbon and is achiral. The passage states that the glycine is not levorotatory (L). Note that this statement does not mean that glycine is dextrorotatory (R), which would require a chiral atom.

Question 19

How do you calculate the pI of a compound having one plateau on the titration curve at 2.5 and another at 9.5?

Answer 19

Using the formula pI = ½(pKa1 + pKa2)

Question 20

A circuit is comprised of a 12-volt battery with three light bulbs with the same resistance. If two of the light bulbs are wired in parallel and are in series with the third light bulb, what happens when one of the parallel light bulbs is unscrewed?

Answer 20

Two of the light bulbs remain lit because even after unscrewing one of the parallel light bulbs, there is still a circuit for current to flow from the positive terminal to the negative terminal of the battery through the two remaining light bulbs.

Question 21

Air is bubbled through distilled water. The solution will have a pH:

Answer 21

Air contains elemental nitrogen as its major component, but elemental nitrogen is essentially inert and is neither an acid nor a base. On the other hand, carbon dioxide can undergo a hydrolysis reaction in liquid water to produce carbonic acid, a weak acid that produces a solution whose pH is less than the pH of water (pH = 7).

Question 22

Which of the following molecules will have the highest Rf value when studied with thin-layer chromatography using a silica plate?
A.

CH3CH2CH2CH2CH3
B.

HOCH2CH2CH2CH3
C.

HOCH2CH2CH2OH
D.

HOOCCH2CH2CH3

Answer 22

ilica is a highly polar molecule; thus, when chromatography is done on a silica plate, a polar substance will move slower on the plate due to polar-polar interactions between the substance and the plate. This means that the Rf value of a polar substance will be smaller than that of a nonpolar substance since the substance will move less on the plate compared to the solvent front than a nonpolar substance would. Of the options given, compound A is the least polar.

Question 23

Solid phase peptide synthesis occurs from?

Answer 23

olid-phase peptide synthesis proceeds in a C-terminal to N-terminal fashion because the C-terminus is bound to the linker throughout the synthetic process. In the absence of a permanent support at one end — as in SP synthesis — amino acids could be added to either terminus.

Question 24

Assuming a 95% yield for each coupling step, what would be the final yield for synthesizing a 10 amino-acid length peptide?

Answer 24

This requires a solid understanding of SP procedure. Each time we add an amino acid to the chain, we get a 95% pure yield for that step. Here, imagine that each coupling step has a 95% yield and that we are running the cycle 10 times, with each cycle being independent from the preceding cycle. Thus, a 10-amino acid peptide would be synthesized in a (0.95)10 = 0.59 = 60% final yield. This can be assured because the passage allows us to assume a 100% yield in each unprotection step. There is no need to calculate it all out. (0.95)2 = 90%, while (0.95)3 = 85%, so you can extrapolate a 10-step process to give around a 50% yield

Question 25

Atherosclerosis, a particular type of arteriosclerosis, usually involves either complete blockage or severe restriction of blood flow due to high cholesterol and buildup of plaque in the arteries. In extreme cases, constricted arteries may collapse under pressure from outside the arteries. This can best be explained by:

Answer 25

the necessary increase in fluid velocity through the constricted arterial sections causing a corresponding drop in fluid pressure.

According to the continuity equation, velocity increases as cross-sectional area decreases. Increasing velocity decreases pressure. If the pressure inside the artery drops far enough, it may fall below the pressure outside the artery, causing it to collapse from external pressure.

Question 26

When a patient is on the operating table for heart surgery, surgeons need to clamp major nearby blood vessels before cutting them because, according to Bernoulli’s equation, a volume of pressurized blood opened to the atmosphere:

Answer 26

will convert its pressure to kinetic energy, rapidly exiting the body and causing shock.

When the surgeons cut into the artery, blood will obviously shoot out of the body as a result of blood pressure. That pressure is converted to kinetic energy, causing the blood to move rapidly as it exits the body.

Question 27

A man is accidentally exposed to a toxin which binds irreversibly and noncompetitively to pyruvate dehydrogenase. A likely consequence of this ingestion is:

Answer 27

Pyruvate dehydrogenase is the enzyme that mediates pyruvate decarboxylation. This step is the critical link between anaerobic and aerobic respiration. With this link broken, cells would be limited to anaerobic respiration. Thus, a decrease in aerobic respiration makes sense in this context.

Question 28

What are the lacteals?

Answer 28

This is a straightforward anatomy question with no information from the passage needed. The lacteals are structures in the intestines associated with absorbing fat into the lymphatic system. This is a straightforward anatomy question with no information from the passage needed. The lacteals are structures in the intestines associated with absorbing fat into the lymphatic system.

Question 29

Contraction of the diaphragm leads to?

Answer 29

Contraction of the diaphragm leads to inspiration. Whereas relaxation of the diaphragm leads to expiration.

Question 30

What is the difference between the maximum and minimum volume of air in the lungs of an 80-kg man?

Answer 30

From the provided figure, the maximum volume held in the lungs is 80 mL/kg, while the minimum is 15 mL/kg. This is a difference of 65 mL/kg, which, for an 80-kg man, amounts to (65 mL/kg)(80 kg) = 5200 mL, or 5.2 L.