Medical Tests Medical Tests Certifications MCAT-TEST Questions & Answers

• Question 161:

  A solar-power collector has an area of 10 cm2 facing the sun. If the intensity of the sunlight incident upon this surface is 1.5 kW/m2, what is the maximum energy the device can supply in one hour?

  A. 1500 J

  B. 15000 J

  C. 5400 J

  D. 54000 J

  Correct Answer: C

  Explanation: We will calculate to determine the energy supplied by the sun to a 10 cm2 region during 1 hour, assuming that the device is 100% efficient.

  

• Question 162:

  A student conducts a chemical analysis of the components of a popular soft drink. The beverage label shows that the drink contains carbonated water, phosphoric acid, caffeine, and caramel color, but does not indicate the concentrations of these chemicals.

  

  Dissolved carbon dioxide will react reversibly with water to form carbonic acid. In an attempt to analyze the beverage composition, the student conducts the following experiments on a one liter sample of the beverage.

  Experiment 1

  The sample is placed in a sealed beaker cooled to 10?C and a vacuum is created in the space above the beverage. The gas pumped from this space is passed through a solution of BaCl2, producing a white precipitate. The process

  continues until no more precipitate forms. The precipitate is dried and found to have a mass of 9.5 grams.

  Experiment 2

  The remaining solution left in the sealed beaker is then titrated with 0.01 M NaOH to give the titration curve shown in Figure 1.

  

  Figure 1

  Which of the following plots best indicates the composition of phosphoric acid in the 1 Liter sample during the titration?

  

  A. Option A

  B. Option B

  C. Option C

  D. Option D

  Correct Answer: C

  During the titration, the phosphoric acid is undergoing the following transitions:

  

  Points A and C are the best buffering regions, as indicated in the titration curve by the lack of change in pH with the addition of NaOH. They are the best buffering regions because they contain equal concentrations of the acid and its conjugate base. So point A has equal concentrations of H3PO4 and H2PO4? and point C has equal concentrations of H2PO4?and HPO42? We can see from the titration curve that point A has a pH of around 2.3 and point C has a pH around 7.5.Looking at the answer hoices, only choice C shows an equal concentration of these species at the given pH values.

• Question 163:

  A hovercraft is a versatile vehicle capable of traveling over land, water, or any other essentially flat surface. The hovercraft consists of a body or hull onto which a rotor (lift fan) is mounted. The lift fan provides the vertical lift by propelling air into an area beneath the hovercraft called the skirt. The pocket of air in the skirt supports the moving hovercraft and reduces the friction between the vehicle and the ground to almost zero. As such, there is no contact between the hovercraft and the ground.

  A second fan, which generates a horizontal thrust, propels the hovercraft forward. Rudders which direct the airflow from this second fan are used by the pilot to control the movement of the hovercraft. The horizontal movement of the

  

  hovercraft is opposed by air resistance which generates aerodynamic drag.

  A 600 kg hovercraft hovers 0.6 meters above the ground. The rectangular hovercraft is 4 meters long and 2 meters wide with a skirt which hangs from the edge to a distance of 4 cm above the ground. What is the average pressure of air in the skirt?

  A. 735 Pa

  B. 980 Pa

  C. 47.040 kPa

  D. 101.735 kPa

  Correct Answer: D

  In order for the hovercraft to hover above the ground, the pressure in the skirt must apply an upward force equal (and opposite) to the gravitational force on the hovercraft. The weight of the hovercraft is given by:

  

  The pressure, which is force per unit area, is therefore:

  

  This pressure, however, is only the gauge pressure: the pressure in excess of atmospheric pressure. The absolute or total pressure under the skirt is:

  

  pressure = gauge

  Note that this choice is the only choice greater than atmospheric pressure. The pressure must be greater in order to lift the hovercraft.

• Question 164:

  According to the reaction coordinate diagram shown below, which of the following forward reactions would proceed most rapidly at high temperatures?

  

  A. A

  B. B

  C. C

  D. D

  Correct Answer: B

  The rate of a reaction is dependent on the activation energy. The lower the activation energy, the more rapid the reaction. Choice B has the lowest activation energy of all of the choices. Note that Reaction B indicates an increase in the total energy of the compounds in the reaction. Although the reaction is not energetically favorable, it is still the most rapid. Do not confuse thermodynamics with kinetics.

• Question 165:

  

  1M NaOH is added to a solution containing 1M A , 1M A , 1M M , and 1M M . Given the solubility data shown below, which of the following will precipitate first?

  

  A. Option A

  B. Option B

  C. Option C

  D. Option D

  Correct Answer: A

  The question asks which will precipitate first. Each metal hydroxide, M(OH)n, has an equilibrium equation of the following form:

  

  Since the concentration of each metal [M] = 1 molar, the equilibrium equation reduces to:

  

  Thus, the saturation concentration of hydroxide ion, in each case, is:

  

  Saturation [OH-] AgOH is saturated at the lowest [OH-] and will therefore precipitate first.

  

  

  

  

• Question 166:

  An object at rest with the shape of an equilateral triangle is subject to three external forces as shown in the diagram. If the object does not exhibit translational motion, what must F and be, respectively?

  

  A. 20 N, 120°

  B. 20 N, 165°

  C. 10 N, 120°

  D. 10 N, 165°

  Correct Answer: B

  This problem can be solved by examining the angles and noting that the two given forces are antiparallel. First, each of the angles in an equilateral triangle is 60°, adding up to the 180° characteristic of all triangles. We know that the forces are antiparallel because they make the same angle, 75°, with a line that intersects both of them. That line is the left edge of the equilateral triangle.

  

  Once we determine that the two given forces are antiparallel, we know that the third force must be applied along the same angle (in order to cancel out with the other two.) Summing the two given forces, we get a net force of 20N to the upper left.

  

  So we know that the answer must be 20N towards the bottom right. This narrows the choices to A and B. Now we must determine the angle. The supplementary angle is 120? as shown below. Knowing that the two forces are parallel, we can calculate the 45? as shown below. This allows us to calculate .

  

• Question 167:

  The nuclei of certain unstable isotopes will spontaneously decay, producing a more stable nucleus and releasing a particle or quantity of energy. Alpha decay releases a helium nucleus, beta decay emits an electron, while gamma decay is the emission of a high energy photon. Each type of radioactive decay is characterized, in part, by the half-life of the radioactive material--the time required for half of the nuclei in a sample to undergo decay. Examples of such decays are shown in Figure 1.

  

  Figure 1 A Geiger counter can be used to detect the decay of radioactive materials. A simple Geiger counter consists of a hollow metal cylinder with a wire along its axis. The cylinder is filled with low pressure argon gas and a high voltage difference is applied between the wire and the cylinder. When alpha, beta, or gamma radiation passes through the cylinder, it interacts with the gas particles and leads to the formation of ions which cause a discharge between the wire and the cylinder.

  The consequent current may be used to drive a speaker, producing the characteristic clicking sound of the Geiger counter each time a pulse of current occurs. The Geiger counter circuitry is shown in Figure 2.

  

  Figure 2

  Which of the following statements is true concerning two isolated radioactive samples examined separately with a Geiger counter?

  A. The sample with the shorter half-life will produce a higher frequency of clicks.

  B. The sample with the longer half-life will produce a higher frequency of clicks.

  C. The sample with the shorter half-life will generate a larger current.

  D. The half-life cannot be determined from the click frequency alone.

  Correct Answer: D

  The half-life indicates the time required for half of a sample to decay and is thus a relative measure of the frequency of decay between two samples of equal mass. However, without knowing the mass, we cannot determine the absolute frequency of decays. A huge sample with a long half-life may produce more decays than a small sample with an extremely short half-life.

• Question 168:

  The nuclei of certain unstable isotopes will spontaneously decay, producing a more stable nucleus and releasing a particle or quantity of energy. Alpha decay releases a helium nucleus, beta decay emits an electron, while gamma decay is the emission of a high energy photon. Each type of radioactive decay is characterized, in part, by the half-life of the radioactive material--the time required for half of the nuclei in a sample to undergo decay. Examples of such decays are shown in Figure 1.

  

  Figure 1

  A Geiger counter can be used to detect the decay of radioactive materials. A simple Geiger counter consists of a hollow metal cylinder with a wire along its axis. The cylinder is filled with low pressure argon gas and a high voltage difference is

  applied between the wire and the cylinder. When alpha, beta, or gamma radiation passes through the cylinder, it interacts with the gas particles and leads to the formation of ions which cause a discharge between the wire and the cylinder.

  The consequent current may be used to drive a speaker, producing the characteristic clicking sound of the Geiger counter each time a pulse of current occurs. The Geiger counter circuitry is shown in Figure 2.

  

  Figure 2

  A Geiger counter is best suited for which of the following applications:

  A. comparing the relative magnitudes of radioactivities of two nuclear waste depositories.

  B. spatially locating a radioactive isotope injected into a patient.

  C. calculating the total energy of a radioactive particle.

  D. determining the identity of various types of radioactivity.

  Correct Answer: A

  A Geiger counter provides a largely qualitative measure of radioactivity in an area.Choice B is incorrect because a Geiger counter cannot locate radioactivity with the precision required for a radioimmuno assay.Choice C is incorrect because a

  Geiger counter does not provide a quantitative measure of the energy of a particle. If the particle has enough energy to produce an ionization, it will produce a click. Any energy beyond this is not detected.

  Choice D is incorrect because a Geiger counter cannot differentiate between different types of ionizing radiation.

• Question 169:

  The nuclei of certain unstable isotopes will spontaneously decay, producing a more stable nucleus and releasing a particle or quantity of energy. Alpha decay releases a helium nucleus, beta decay emits an electron, while gamma decay is the emission of a high energy photon. Each type of radioactive decay is characterized, in part, by the half-life of the radioactive material--the time required for half of the nuclei in a sample to undergo decay. Examples of such decays are shown in Figure 1.

  

  Figure 1

  A Geiger counter can be used to detect the decay of radioactive materials. A simple Geiger counter consists of a hollow metal cylinder with a wire along its axis. The cylinder is filled with low pressure argon gas and a high voltage difference is

  applied between the wire and the cylinder. When alpha, beta, or gamma radiation passes through the cylinder, it interacts with the gas particles and leads to the formation of ions which cause a discharge between the wire and the cylinder.

  The consequent current may be used to drive a speaker, producing the characteristic clicking sound of the Geiger counter each time a pulse of current occurs. The Geiger counter circuitry is shown in Figure 2.

  

  Figure 2

  Beta radiation differs from gamma rays in the following way:

  A. gamma rays can penetrate the Geiger counter cylinder, while beta rays cannot.

  B. beta particles and gamma rays will be deflected in opposite directions by a magnetic field.

  C. beta particles and gamma rays will be deflected in opposite directions by an electric field.

  D. beta particles will be deflected in a magnetic field while gamma rays will not.

  Correct Answer: D

  Beta particles have a negative charge. They are electrons, as shown in Figure 1 of the passage. Beta particles travelling up in the plane of the page will be deflected to the left by a magnetic field directed out of the plane of the page. Gamma rays are high energy photons lacking any charge. They will not be deflected in a magnetic field or an electric field precisely because they are uncharged.

• Question 170:

  The nuclei of certain unstable isotopes will spontaneously decay, producing a more stable nucleus and releasing a particle or quantity of energy. Alpha decay releases a helium nucleus, beta decay emits an electron, while gamma decay is the emission of a high energy photon. Each type of radioactive decay is characterized, in part, by the half-life of the radioactive material--the time required for half of the nuclei in a sample to undergo decay. Examples of such decays are shown in Figure 1.

  

  Figure 1

  A Geiger counter can be used to detect the decay of radioactive materials. A simple Geiger counter consists of a hollow metal cylinder with a wire along its axis. The cylinder is filled with low pressure argon gas and a high voltage difference is

  applied between the wire and the cylinder. When alpha, beta, or gamma radiation passes through the cylinder, it interacts with the gas particles and leads to the formation of ions which cause a discharge between the wire and the cylinder.

  The consequent current may be used to drive a speaker, producing the characteristic clicking sound of the Geiger counter each time a pulse of current occurs. The Geiger counter circuitry is shown in Figure 2.

  

  Figure 2

  The half-life of 32P is 14.28 days. What fraction of an initially pure sample will have decayed after 28.56 days?

  A. 1/4

  B. 1/2

  C. 3/4

  D. 1

  Correct Answer: C

  

  After two halflives (28.56 days), 3/4 of the sample will have decayed. in the first half life, and

  

  in the second. Only of the sample will remain undecayed. In other words. remains. Therefore is gone.