Day 47 MCAT Practice Question

Passage 7: Sound

Sound is critically important in marine ecosystems as a method of communication

for animals, submarines, and other technological instruments. Researchers

conducted an experiment to study sound waves in various aquatic contexts, with a

special focus on the speed of sound across varying media.



A speaker emitting high-frequency sound was utilized to generate sound waves at

a fixed frequency. Hydrophones, strategically placed at varying distances from the

radio, measured sound intensity and speed in freshwater, salt water, and air.

The first phase of experimental data collection involved measuring the speed of

sound in these three media at the same temperature. Results showed that there

was a significant difference between all three, with the most significant difference

between either water medium and air. Next, researchers varied the temperature

and salinity of the water in the tanks, measuring the speed of sound at regular

increments.



They also used ultrasound waves to map the seafloor, detecting obstacles. Findings

are tabulated in Table 1:

Attenuation in signal intensity was attributed to absorption and scattering of waves

in the water (as signal intensity decreased with increasing depth). Background noise

in the water column affected the precision of the measurements; regions with high

biological activity reduced measurement accuracy.

D-glucose is dissolved in water and undergoes mutarotation, a process in

which it interconverts between its alpha and beta anomers. The solution

reaches equilibrium at 25°C, wherein the final solution is 36% alpha-D-glucose.

(The specific rotation of pure alpha-D-glucose is +112°, and that of pure betaD-glucose is +19°) What is the specific rotation of the equilibrium mixture of

D-glucose at 25°C?

A) +112°

B) +65.3°

C) +52.5°

D) +19