SAT2考试物理题型讲解.

SAT II Physics is a one-hour-long test composed of 75 questions anddivided into two parts. You can answer questions in any order you like,though you’re less likely to accidentally leave a question out if you answer them in the order in which they appear. Part A—classification questions—takes up the first 12 or 13 questions of the test, while PartB—five-choice completion questions—takes up the remaining 62 or 63questions. Part A: Classification Questions Classification questions are the reverse of normal multiple-choice question: they give you the answers first andthe questions second. You’ll be presented with five possible answerchoices, and then a string of two to four questions to which thoseanswer choices apply. The answer choices are usually either graphs orthe names of five related laws or concepts. Because they allow forseveral questions on the same topic, classification questions will askyou to exhibit a fuller understanding of the topic at hand. The level of difficulty within any set ofquestions is generally pretty random: you can’t expect the firstquestion in a set to be easier than the last. However, each set ofclassification questions is generally a bit harder than the one thatcame bore. You should expect questions 11–13 to be harder thanquestions 1–4. Classification Question Example Directions: Each set oflettered choices below rers to thenumbered questions immediatelyfollowing it. Select the one letteredchoice that best answers eachquestion and then blacken thecorresponding space on the answer sheet.A choice may be used once, morethan once, or not at all in each set. Questions 1–3

A boy throws a ball straight up in the air and then catches it again. 1. Which of the above graphs best represents the ball’s position with respect to time? 2. Which of the above graphs best represents the ball’s velocity with respect to time? 3. Which of the above graphs best represents the ball’s acceleration with respect to time? Explanation You can usually answer classification questionsa bit more quickly than the standard five-choice completion questions,since you only need to review one set of answer choices to answer aseries of questions. The answer to question 1 is B. The ball’s position with respect to time can be expressed by the equation y = –1/2 gt2, where g is the downward, acceleration due to gravity. As we can see, the graph of y against tis an upside-down parabola. In more intuitive terms, we know that, overtime, a ball thrown in the air will rise, slow down, stop, and thendescend. The answer to question 2 is E. Theacceleration due to gravity means that the velocity of the ball willdecrease at a steady rate. On the downward half of the ball’strajectory, the velocity will be negative, so E, and not A, is the correct graph. The answer to question 3 is D. Theacceleration due to gravity is constant throughout the ball’strajectory, and since it is in a downward direction, its value isnegative. Don’t worry if the question confused you and theexplanations didn’t help. This material and more will be covered inChapter 2: Kinematics. This was just an exercise to show you how aclassification question is formatted. Part B: Five-Choice Completion Questions These are the multiple-choice questions we allknow and love, and the lifeblood of any multiple-choice exam. You knowthe drill: they ask a question, give you five possible answer choices,and you pick the best one. Got it? Good. An example appears below. While you’ll often find two or three questionsin a row that deal with the same topic in physics, there is no pattern.You might find a question on modern physics followed by a question ondynamics followed by a question on optics. However, there is a generaltendency for the questions to become more difficult as you progress. Five-Choice Completion Question Example Directions: Each of thequestions of incomplete statementsbelow is followed by five suggestedanswers or completions. Select theone that is best in each case andthen fill in the corresponding oval onthe answer sheet. 1. A gas in a closed container is steadily heated over a period of time. Which of the following statements is true of this process? (A)The average kinetic energy of the gas molecules decreases (B)The mass of the container increases (C)The pressure exerted by the gas on the walls of the container increases (D)The gas changes phase into a liquid (E)The specific heat of the gas decreases Explanation The answer to this question is C. The key lies in remembering the ideal gas law: PV = nRT. According to this formula, an increase in temperature is accompanied by an increase in pressure. Ais wrong, since the average kinetic energy of gas molecules correspondsto their temperature: if the temperature increases, so does the averagekinetic energy of the molecules. B is wrong because we’re dealing with a closed container: the mass cannot either increase or decrease. D is wrong because a gas must be cooled, not heated, to change phase into a liquid. Finally, Eis wrong because the specific heat of any substance is a constant, andnot subject to change. We’ll touch on all this and more in Chapter 9:Thermal Physics.