Passage VI
Three studies examined how the volume of runoff from melting ice is affected by wind speed and by the presence of sand beneath the ice.
In a lab kept at 18°C, runoff was collected from a plastic box containing melting ice. The box was tilted at 10° and had horizontal openings in its lower end. After flowing through the openings, the runoff fell into a trough (see diagram) and was conveyed to a measuring device.
Study 1
In each of the first 3 of 4 trials, the following steps were carried out:
1. A 30 cm deep layer of a particular clean, dry sand was placed in the box.
2. A 30 cm deep layer of chipped ice (density 0.4 g/cm3) was placed in the box on top of the layer of sand.
3. A fan was turned on to blow air at a constant speed onto the trough end of the box.
4. For the next 600 min, the volume of runoff collected over each 20 min period was measured.
The wind speed was 2.5 m/sec, 1.0 m/sec. and 0.5 m/sec in the first, second, and third trials, respectively.
In the fourth trial, all steps except Step 3 were carried out. (The fan was not turned on.)
The results of the 4 trials are shown in Figure 1.
Study 2
The second trial of Study 1 was repeated. Then the second trial of Study 1 was again repeated, except that Step 1 was omitted. (No sand layer was placed in the box.) The results of the 2 trials are shown in Figure 2.
38. The volume of runoff measured at 200 min in Study 1 for the 4 wind speeds is best represented by which of the following graphs?
Your Answer is
Correct Answer is J
Explanation
Looking at figure 1, when the abscissa is 200 msec, the ordinates of wind speeds 1.0 and 0.5 are equal, so F & G are excluded;
Look at this time, the ordinate of wind speed 2.5 is the smallest , so choose J