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Test Prep MCAT Test Exam
Medical College Admission Test: Verbal Reasoning, Biological Sciences, Physical Sciences, Writing Sample (Page 21 )

Updated On: 30-Jan-2026
Page 21 of 164
PDF with 811 Questions

When softball players take batting practice, they often use a machine called an "automatic pitcher," which is essentially a cannon that uses air pressure to launch a projectile. In a prototype automatic pitcher, a softball is loaded into the barrel of the cannon and rests against a flat disk. That disk is locked into place, and a high air pressure is built up behind it. When the disk is released, the softball is pushed along the barrel of the cannon and ejected at a speed of V0.
Figure 1 shows the batter and automatic pitcher. The angle of the barrel to the horizontal is . The unit vectors i and j point in the horizontal and vertical directions respectively.

Figure 1
The height above the ground y of the softball as a function of time t is shown in Figure 2, where t = 0 at Point A, t = tB at Point B, and t = tC at Point C. The softball is ejected from the barrel of the cannon at Point A; it reaches its maximum height at Point B; and the batter hits the softball at Point C. (Note: Assume that the effects of air resistance are negligible unless otherwise stated.)

Figure 2
How does the work done by the automatic pitcher change as the angle of the barrel to the horizontal increases?

  1. The work done increases, because the softball's maximum height increases.
  2. The work done decreases, because the softball lands closer to the cannon.
  3. The work done does not change, because the air pressure behind the disk is unchanged.
  4. The work done does not change, because gravity is a conservative force.

Answer(s): C

Explanation:

The softball starts off at rest and acquires a speed v0 as it is launched from the cannon. The work-energy theorem states that the work done equals the change in the kinetic energy. Since the softball acquires a kinetic energy equal to (1/2)mv0 , the automatic pitcher must have done work on it. The pitcher uses air pressure, which builds up behind a disk, to do the work when the disk is released. The angle of the barrel to the horizontal will not affect this mechanism, and the softball will still be ejected with the same kinetic energy. Hence, the work done by the pitcher does not change and choice C is correct.
Although it is true that the softball's maximum height increases and that the distance it lands from the cannon decreases, the work done by the pitcher does not change, so choices A and B are wrong. Although it is also true that gravity is a conservative force, it is irrelevant because the question asks about the work done by the pitcher, not the work done by gravity. Hence, choice D is incorrect as well.



There are two opposing theories of light: the particle theory and the wave theory. According to the particle theory, light is composed of a stream of tiny particles that are subject to the same physical laws as other types of elementary particles. One consequence of this is that light particles should travel in a straight line unless an external force acts on them. According to the wave theory, light is a wave that shares the characteristics of other waves. Among other things, this means that light waves should interfere with each other under certain conditions.
In support of the wave theory of light, Thomas Young's double slit experiment proves that light does indeed exhibit interference. Figure 1 shows the essential features of the experiment. Parallel rays of monochromatic light pass through two narrow slits and are projected onto a screen. Constructive interference occurs at certain points on the screen, producing bright areas of maximum light intensity. Between these maxima, destructive interference produces light intensity minimA. The positions of the maxima are given by the equation d sin = n, where d is the distance between the slits, is the angle shown in Figure 1, the integer n specifies the particular maxima, and is the wavelength of the incident light. (Note: sin tan for small angles.)

Figure 1
What is the angle for the third maximum (n = 3)?

  1. 3 × 10-5 radians
  2. 3 × 10-3 radians
  3. 0.3 radians
  4. 0.3 degrees

Answer(s): B

Explanation:

To solve this problem, apply the formula given in the passage which quantifies the positions of the intensity maximA. The formula is d sin = n, where d is the distance between the slits, is the angle, and is the wavelength. The note in the passage says that sin when is small.
You have to know that this approximation is only valid when is measured in radians. Making this approximation, we obtain d = n, and solving for we obtain = n/d. Note that the distance units of and d can be anything as long as they are the same. n is given in the question stem, and and d are given in Figure
1. Substituting, we obtain



There are two opposing theories of light: the particle theory and the wave theory. According to the particle theory, light is composed of a stream of tiny particles that are subject to the same physical laws as other types of elementary particles. One consequence of this is that light particles should travel in a straight line unless an external force acts on them. According to the wave theory, light is a wave that shares the characteristics of other waves. Among other things, this means that light waves should interfere with each other under certain conditions.
In support of the wave theory of light, Thomas Young's double slit experiment proves that light does indeed exhibit interference. Figure 1 shows the essential features of the experiment. Parallel rays of monochromatic light pass through two narrow slits and are projected onto a screen. Constructive interference occurs at certain points on the screen, producing bright areas of maximum light intensity. Between these maxima, destructive interference produces light intensity minimA. The positions of the maxima are given by the equation d sin = n, where d is the distance between the slits, is the angle shown in Figure 1, the integer n specifies the particular maxima, and is the wavelength of the incident light. (Note: sin tan for small angles.)

Figure 1
Which of the following supports the particle theory of light?

  1. The energy of light is quantitized.
  2. Light exhibits interference.
  3. Light is subject to the Doppler effect.
  4. No particle can have a speed greater than the speed of light.

Answer(s): A

Explanation:

If a quantity is quantized, it means that there is a fundamental unit of that quantity which cannot be further divided. For example, charge is quantized, so charges only appear in nature as multiples of the fundamental charge e. There is not a continuous range of values for the possible charge on an object. Similarly, light energy is quantized. The fundamental unit of light energy is called a photon. The photon, because it cannot be subdivided, is similar to other elementary particles. Thus, quantization implies particle-like characteristics, and choice A is correct.
The passage states that the wave theory, not the particle theory, predicts that light will exhibit interference, so choice B is incorrect. The Doppler effect refers to the change in frequency observed when a wave source or detector is in motion. That the Doppler effect occurs with light as well as sound waves indicates that light has wave, not particle, characteristics and choice C is wrong. Neither particles nor waves can travel faster than the speed of light, so the fact that particles cannot travel faster than light does not support or weaken the particle theory and choice D is wrong.



A deep-sea research module has a volume of 150 m3. If ocean water has an average density of 1,025 kg/m3, what will be the buoyant force on the module when it is completely submerged in the water? (Note: The acceleration due to gravity is 9.8 m/s2.)

  1. 9.8 N
  2. 60 N
  3. 1 × 103 N
  4. 1,5 × 106 N

Answer(s): D

Explanation:

Archimedes' principle states that the buoyant force exerted by a fluid on a submerged object is equal to the weight of the fluid displaced. In this case, the submerged object is the research module and the fluid is ocean water. Mathematically, the buoyant force is given by F = mwg, where mw is the mass of the water and g is the acceleration due to gravity. Since we are not given the mass of the water displaced, we express it as mw = pwVw, where pw is the density of the water and Vw is the volume of the water displaced. But the volume of the water displaced is identical to the volume of the submerged module, V0. Hence, mw = pwVw = mw = pwV0, and
F = mwg = pwV0g. Since the answer choices are far apart, we round off the values given in the question and calculate
F= pwV0g (1,000 kg/m3 )(150 m3)(10 m/s2 ) = 1.5 × 106 N.



A researcher in a molecular biology lab planned to carry out an extraction procedure known as an alkaline plasmid prep, which is designed to purify plasmids, small pieces of the hereditary material DNA, from bacterial cells. The bacteria are first placed into a test tube containing liquid nutrient medium and allowed to grow until they reach a high population density. The culture, which consists of solid cells suspended in the medium, is then centrifuged; a solid pellet is formed. The supernatant is poured out, leaving the pellet behind, and the cells are resuspended in a mL of lysis buffer solution (50 mM glucose, 25 mM Tris buffer and 10 mM ethylenediaminetetraacetic acid (EDTA), with 5 mg of the enzyme lysozyme added). They are then incubated for 30 minutes at 0° C, during which time the bacterial cell walls break down and the cell contents are released into the solution. After incubation, 1 mL of 0.4 N sodium hydroxide and 1 mL of 2% sodium dodecyl sulfate (SDS) are added, and the solution is again incubated on ice for 10 minutes. 2 mL of 3 M sodium acetate are added and the mixture is incubated for 30 minutes at 0° C. The test tube is centrifuged once more and the supernatant is decanted into a clean tube, leaving behind the protein and most other cell components in the pellet.
Finally, 10 mL of pure ethanol are added to the supernatant from the previous step to precipitate out the DNA, and the test tube is incubated at -20° C for 60 minutes, during which the mixture remains liquid. The mixture is centrifuged a final time and the supernatant removed. The translucent precipitate that results is washed with 70% ethanol (70% ethanol and 30% water by volume), allowed to dry, and resuspended in 1 mL of TE buffer (10 mM Tris, 1 mM EDTA).
In preparation for this experiment, the researcher prepared stock solutions of the various chemicals that she will need in the experiment. Stock solutions are highly concentrated solutions of commonly used chemicals in water from which dilute solutions are prepared for daily use. Table 1 shows the chemicals, their molecular formulas and weights, and the composition of commonly used stock solutions.


Pure ethanol (CH3CH2OH) is difficult to prepare and therefore expensive; 95% ethanol is much cheaper. Consequently, 95% ethanol is generally used in the preparation of dilute ethanol solutions. How much 95% ethanol would be needed to produce a 500 mL solution of 70% ethanol by volume in water?

  1. 333 mL
  2. 350 mL
  3. 368 mL
  4. 475 mL

Answer(s): C

Explanation:

The easiest way to do it is to figure out how much ethanol is in the solution at the end of the dilution, and work backwards from the end. Now, notice that the meaning of the percentage sign in this question and in the preceding question is different ­ there we were talking about percentage by mass, whereas this question tells you clearly that it's dealing with percentage by volume. Also, you're told in the passage that a 70% ethanol solution contains 70% ethanol and 30% water by volume. In practice, this is how researchers do usually measure solutions, just for convenience ­ it's easiest to measure liquids by their volume and measure solids by their mass. Anyway, 500 milliliters of a 70% ethanol solution will contain 350 milliliters of ethanol and 150 milliliters of water. So we need an amount of 95% ethanol that contains 350 milliliters of ethanol. If we call this amount X, then 0.95X equals 350 milliliters. So we want a choice that's just a little more than 350, and the only one that fits is C. Sure enough, if we solve the equation, we find that X equals 368 milliliters, choice C.



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