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28. A person sits at rest on the floor. What two vertical forces act upon the person? Do these two forces constitute an action/reaction pair as defined by Newton's third law of motion? A. normal force and static friction; yes, an action/reaction pair B. kinetic friction and weight; not an action/reaction pair C. weight force and normal force; not an action/reaction pair D. weight force and normal force; yes, an action/reaction pair 29. The loudness (or intensity) of a sound wave is related to its A. duration. B. frequency. C. wavelength. D. speed E. amplitude 30. Diffraction is most prominent when a wave encounters an obstacle whose size is A. less than the wavelength of the wave B. greater than the wavelength of the wave C. comparable to the wavelength of the wave D. none of the above 31. A student plays on a see-saw with her experimental android robot, Robby. The student has a weight of 275 N and is seated 2.5 m from the axis of rotation. Robby balances her when he is seated 0.7 m from the axis. What is the magnitude of the net torque acting on the seesaw? A. 740 Nm B. 668 Nm C. 687 Nm D. O Nm E. none of the above 32. The diagram shows a pulse moving to the right in a rope. Point A is a point on the rope. Which arrow best shows the direction of the movement of point A on the rope? A. B. E