ACT真題每日一練12.23

　　Science Question for Wednesday, December 23rd, 2015

　　Passage II

　　The Sun's path from sunrise to sunset varies with the time of year. A student performed the following experiments on three clear, sunny days at three- or four-month intervals throughout the course of a year to study the path of the Sun through the sky.

　　Experiment 1

　　At a chosen Northern Hemisphere location, the student placed a stick vertically into the ground so that 1 meter of its length was left above ground. The student knew that the length of the shadow was related to the height of the Sun above the horizon and that the shadow would point away from the direction of the Sun. The length in meters (m) and direction of the shadow cast by the stick were measured one hour after sunrise (Shadow A), at mid-morning (B), at noon (C), at mid-afternoon (D), and one hour before sunset (E) on each of the three days. The direction of each shadow was determined by placing a magnetic compass at the base of the stick and aligning the north arrow with the north mark on the compass. The direction of each shadow was then determined by a comparison with the compass face markings. The results are recorded in Table 1.

　　Experiment 2

　　The following year, the student repeated Experiment 1 at a chosen location in the Southern Hemisphere. The results are in Table 2.

　　When the Sun is at an altitude 45° above the horizon, a vertical object will cast a shadow with a length equal to the object’s height. Which of the following days included a measurement taken when the Sun was at an altitude of 45° ?

　　A. Day 1 in Experiment 1

　　B. Day 1 in Experiment 2

　　C. Day 2 in Experiment 1

　　D. Day 3 in Experiment 2

　　謎底：D

　　【剖析】Since 1.0 meter of the stick was exposed above ground in the experiments, one would look for a set of measurements that included a shadow length of exactly 1.0 meter. Shadow C on this day was exactly 1.0 meter long.

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