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# Sample MCAT Questions: Physical Sciences

PHYSICAL SCIENCES
33 QUESTIONS
45 MINUTES

DIRECTIONS:

The following questions or incomplete statements are in groups. Preceding each series of questions or statements is a paragraph or a short explanatory statement, a formula or set of formulas, or a definition. Read the written material and then answer the questions or complete the statements. Select the ONE BEST ANSWER for each question and indicate your selectionby marking the corresponding letter of your choice on the Answer Form. Eliminate those alternatives you know to be incorrect and then select an answer from among the remaining alternatives. You may consult a periodic table if needed.

Passage I (Questions 31-36)

A human centrifuge is used to test and train pilots and astronauts to withstand the large "g-forces" experienced during flight. The centrifuge arm length is such that the subject moves in a large circle of radius 9 m. The maximum angular velocity is 4 radians/sec. The subject normally faces inward toward the center of the circular path. ("eyeballs in").

During a test, the subject's respiratory and metabolic rate rise. The energy released per liter of oxygen consumed in human metabolism averages about 20,000 J/L.

31. What is the maximum linear (tangential) speed of the subject along the circular path at the maximum angular velocity of 4 radians/s?

A. 18 rn/sec                 C. 36 m/sec
B.  25 m/sec                 D. 226 rn/sec.

32. A pilot of mass 82 kg (180 lbs) experiences 8 "g's" during one test for a period of 2 minutes. What is centripetal force, innewtons, acting on the pilot?

A. 16N                   C. 960N

B. 660N                 D. 6400N

33. In the earth frame of reference, what centrifugalforce acts on the pilot during the test?

A.  The centrifugal force on the pilot is equal and opposite the centripetal force on the pilot.
B.  The centrifugal force on the pilot is 1 "g" larger than the centripetal force on the pilot.
C. The centrifugal force on the pilot is 1 "g" smaller than the centripetal force on the pilot.
D. There is no centrifugal force on the pilot

34. The pilot's metabolic rate rises to 450 W and remains at that level during the 2 minute test period. What is the approximate number of liters of oxygen consumed by the pilot during the test period?

A. 3L                                   C. 6L

B. 4L                                   D. l0 L

35. What force acts on the back of the pilot's seat?

A. 0 N                                C. 960N

B. 88N                               D. 6400 N

36. The pilot now faces outward ("eyeballs out"). What effect does this have on the centripetal force acting on the pilot?

A. The centripetal force now points outward.

B. The seat back now exerts an outward force.

C. The centripetal force is replaced by the centrifugal force (now supplied by the pilot's seat harness).

D. The centripetal force is unchanged (now supplied by the pilot's seat harness).

Passage II (Questions 37-41)

A brewery builds a cylindrical tank with 12 large electrical resistance heaters for the purpose of boiling city water to obtain distilled water. Each heater has a resistance of 15 ohms and normally draws a 20 Acurrent. The tank radius is 1.1 m and the normal depth of water will be 2.0m. An access hatch of 30 cm radius is designed to withstand a maximum gaugepressure of 31,000 N/rn2. When the tank is full the water pressureon the tank bottom is normally 19,500 N/rn2 when the tank is opento the air at I atm (1 atm = 1.01 x 105 Nim2). The tank can bepressurized so that the water will boil at a higher temperature than I 000 C.

37. The tank is filled to the normal 2 m depth and then pressurized so that the maximum gauge pressure of 31,000 N/rn2 is exerted on the tank bottom. Of this maximum pressure, how much is dueto pressurization?
A. 126,300 N/rn2                        C. zero

B. 8200N/m2                               D. 11,400 N/rn2

38. What total electrical power, in watts, is supplied to all 12 resistance heaters at a current of 20 A?
A. 40,000 W                               C. 49,000W

B 72,000W                                 D. 52,000 W

39. What is the normal water volume in the cylindrical tank?
A. 7.6 m3                              C. 6.5 rn3

B. 4.2 m3                               D. 14.1 m3

40. The water enters the tank at 500C and boils at 1050C due to pressurization. If the current is increased until the 12 heaters are supplying 110,000 watts, how long will it take 5 m 3 (mass = 5,000 kg) of water to heat through the 55 0C rise? The heat needed to change the temperature of 1 kg of water by 10 C is its "specific heat" (c = 4190 joules/kg 0C).

A. 1.5 hours                               C. 2.9 hours

B. 3.4 hours                               D. 6.2 hours

41. The tank can be filled to the normal 2 m depth (and volume) in 13 minutes by a pipe through which the fill water flows at a speed of 1.0 rn/sec. What is the cross-sectional area of the cylindrical fill pipe?

A.  1.1m2                               C. 0.05 m2
B.  0.01 m2                             D. 0.9 m2

Question 42-48 are independent of any passage and of each other.

42. Small spheres of aluminum and lead, both of radius 2.0 cm, are suspended from strings and lowered into a container of waterof density 1000 kg/rn3. The density of aluminum is 2700 kg/rn 3 and of lead, 11,300 kg/rn3. The buoyant forces exerted on aluminum and lead are, respectively:

A. 0.2 N and 0.5 N
B. 0.5 N and 0.2 N
C. 0.33 N and 0.33 N
D. 0.33 N and 0.2 N

43. A car starts from rest with an acceleration of 6 rn/sec 2. What will be its velocity after it has traveled a distance of 12 m?

A. 12 rn/sec                        C. 21 rn/sec

B. 72m/sec                          D. 144m/sec

44. A 6 cm tall object is 20 cm in front of a converging lens of focal length f = +10cm. Find the height of the image and state whether it is a real or virtual image.

A. 6 cm tall, real image

B. 12 cm tall, virtual image

C. 12 cm tall, real image

D. 6 cm tall, virtual image

45. The pressure on an enclosed gas is kept constant while it expands to double its original volume. What change, if any, happens to the absolute temperature of the gas?   A. T doubles also.

B. T decreases by 50%.

C. T increases by 50%.

D. T remains constant also.

46. A resistor in an electric circuit operates at a power level of 6 watts when the applied voltage is 100 volts. If the voltage is doubled to 200 volts, what power is consumed by the resistor? (Assume that the resistance is constant.)

A. 12 watts                                C. 60 watts

B. 3 watts                                  D. 24 watts

47. A spring compressed between 2 carts of unequal masses is released by burning a string and gives the 2-cart system a total kinetic energy KT = K1 + K2, where K1 and K 2 are the individual kinetic energies of the carts. Suppose m1 = 2m2; how do the values of K1 and K2 compare?

A. K2=K1                                       C. K2 =K1/4

B. K2=K1 /2I                         D. K2=2K1

48. A constant force of 8 N acts on a 2 kg mass on a rough surface and a friction force of 4 N opposes the motion. If the mass has an initial velocity of 3 rn/sec, how far will the mass slide in 3 sec?

A.18m                                C. 12m

B. 36m                               D. 32m

Passage III (Questions 49-53)

A solution of AgNO3 (1 x 10-6 molar) is prepared. To this is added K2CrO4 until precipitation of Ag2CrO4 begins. The Ksp of Ag2 CrO4 is 9 X 10-12.

49. The precipitate begins at a K2CrO4 concentration of about:

A. 1 x 10-6.                                        C. 1 x 10-1.

B. 1 x l0-3.                                         D. 1 x 101.

A.. additional precipitation of Ag2CrO4. B. a reaction that will dissolve the Ag2CrO 4 precipitate
C. precipitation of AgCl only if its Ksp is exceeded.
D. A and C.

51. Increasing the temperature will usually:

A.. bring about more complete precipitation.

B. change the Ksp

C. change the formula of the precipitate.

D. not be easily accomplished until ongoing precipitation is complete.

52. If the Ksp ‘s of AgBr, AgCI, and AgI are respectively 7.7 x 10-13, 1.56 x 10-10, and 1.5 x 10-16, the addition of the sodium salt of which of these halides wouldfirst bring about precipitati6n of an insoluble salt? A. NaBr

B. NaCl

C. NaI

D. all about the same (within a factor of 10)

53. If the sodium salts of the 3 halides in question 52 were added to a concentration that is one-half of that needed to bring about precipitation of that particular silver salt, the result would be:   A. precipitation of only the least soluble silver halide.

B. precipitation of part of each of the three silver halides

C. precipitation of' a portion of the two least soluble silver halides.

D. no precipitation.

Passage IV (Questions 54-58)

Many metals react with oxygen to form oxides. Some ofthese oxides, such as Na2O, CaO, and SrO, react with water toform basic solutions. (These oxides are called basic oxides or basic anhydrides.)

Many nonmetals can react with oxygen to form oxides as well. These nonmetal oxides, however, react with water to form acidic solutions. Thus they are called acid anhydrides.

54. Phosphorus would be expected to react with oxygento form an oxide that will:

A. react with water to form an acidic solution.

B. react with water to form a basic solution.

C. react with water to form a neutral solution         D. not react with water.

55. Nitrogen will react with oxygen to form an oxide (N 205) that will:

A. react with water to form an acidic solution.

B. react with water to form a basic solution.

C. react with water to form a neutral solution.

D. not react with water.

56. One mole of Ca will react with oxygen to form an oxide that will react with water to form:   A. one mole of acid in solution.

B. one mole of base in solution.
C. two moles of acid in solution.
D. two moles of base in solution.

57. The solution in the question would require _________for neutralization. A. one mole of HCI

B. one mole of NaOH

C. two moles of HCl

D. two moles of NaOH

58. Burning of coal (without use of sufficient scrubbers) in the production of electricity is believed by many to be a major causeof "acid rain." If so, this is most likely because of the production of:   A. oxides of sulfur.

B. carbon dioxide.

C. carbon monoxide.

D. sodium oxide.

Passage V (Questions 59-63)

Colligative properties of solutions are those proper- ties that depend on the concentration of molecules or ions in solution rather than on their identities.

59. The freezing point of 1000g of water would be lowered most by the addition of one mole of:

A. ethylene glycol. C. Na2S04.
1. sodium chloride. D. ethyl alcohol.

60. Calculations of freezing point depression resulting from solutes are based on:

A. molarity C. mole fraction.

B. molality. D. A and B

61. Colligative properties include:   A. boiling point elevation.

B. freezing point depression.

C. osmotic pressure.

D. more than one of the above.

62. It is noted that the addition of 46g of a solute to 1000g of water will lower the freezing point of water to -20C. It could be predicted that the addition of 92g of the same solute to an identi cal 1000g of water in another container will:   A. lower the freezing point to -40C.

B. lower the freezing point to-8 0C.

C. produce a freezing point of 00C.

D. produce a freezing point of +2 0C.

63. Several beakers are prepared, containing l000g of the same solvent in each. Five grams of nonionizing solutes are added, one solute to each beaker. The greatest effect on boiling point will be noticed with the solute with the: A. highest molecular weight.

B. highest melting point.

C. lowest molecular weight.

D. lowest melting point.

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