Passage III
Suppose a ball is dropped from a height H above a horizontal surface. The ball falls straight down until it collides with the surface; then it bounces straight up, attaining a maximum height y before it begins to fall again. The coefficient of restitution, C, for the collision equals 
.
Therefore:
y=CH
Physics students went to a high-altitude laboratory conduct studies of C for various balls bouncing off different horizontal surfaces. The air temperature and air pressure were constant in the laboratory throughout the studies.
Study 1
The students dropped a racquetball from various H onto a particular horizontal surface, and after each drop they measured y. Then they graphed y versus H(see Figure 1); C equaled the slope of the graph.
The students repeated the procedure in Study 1 and determined C for various balls dropped onto both a bare concrete surface and a concrete surface covered with a thin layer of foam. Both surfaces were horizontal. The results are given in Table 1.
14. To determine if the surface tested in Study 1 was more likely bare concrete or foam-covered concrete, one would compare C in Study 1 with each C in Study 2 for the:
Your Answer is
Correct Answer is F
Explanation
When comparing and studying a specific variable, it is not necessary to ensure that other variables are consistent. Because racquetball was used in Study 1, racquetball must be used in the comparison experiment