2. in which of the following conditions would a person not hear an echo?
o a. the reflecting source is approximately 21.5 meters from the person.
o b. a sound wave reaches the ear, and the reflected wave reaches the ear less than 0.1 seconds later.
oc. a person is standing in the range of the sound waves coming from the original sound source as well as the reflected waves.
o d. a person is standing 30 meters in front of the reflecting surface.

answer would be letter choice (a),   a ball resting on a shelf. would be another example of potential energy   >   stored energy > not moving.

a ball spinning on a finger   >   kinetic energy > moving energy

a ball rolling on the ground   >   kinetic energy   > moving energy

a   ball flying through the air   > kinetic energy   >   moving energy

hope that                                         : )

the answer is c. the lower legs are levers, and the knees are fulcrums. the ankles hold the loads.