Passage IV
Scientists studied the speed of the wind and the size of sand grains at 4 sites on a sand dune (see diagram). At each site, 4 anemometers (devices for measuring wind speed) were attached to a vertical pole at different heights above the ground , and a sand trap was placed at the base of the pole. Each trap could collect only windblown sand grains having diameters from 0.0625 mm to 0.5 mm.
Study
Over a particular 45 min period, wind speed was measured multiple times by each anemometer and sand was collected at all 4 sites
The average wind speed at each anemometer for the 45 min period was calculated . Then each average wind speed was converted to a relative wind speed. (The relative wind speed at an anemometer equaled the average wind speed at the anemometer divided by the average wind speed 12.0 m above the ground at the dune crest site for the same period.) The results are shown in Figure 1.
The mass of the sand collected at each site was measured. Then the sand from each site was sifted through a stack of 12 screens to separate the grains into 13 portions according to diameter. (Each screen had uniform openings of a smaller diameter than the openings in the screen above.) The percent of the sand's mass from grains making up each of the 13 portions was determined (see Figure 2).
21. According to Figure 1, at the interdune site , as anemometer height above the ground increased, relative wind speed:
Your Answer is
Correct Answer is A
Explanation
Looking at the diagram of interdune in figure 1, it is found that as the height of the ordinate increases, the wind speed also increases