Hi, and thank you for your time to read this. I'm having a difficult time figuring out the answer to this question; Q: A porpoise swims toward a school of fish and emits a high pitched sound. The porpoise listens for the echo of its own squeak. I have to predict whether the observer will experience an increase or a decrease in the observed frequency of the sound. Here's my opinion. A: Since the distance to be covered by each wave is decreased by the motion of the source of the sound, the number of waves that strike the porpoise's eardrum in a second will increase and be interpreted as a higher frequency. Could anyone correct me if I'm wrong? or not going the right way? Thanks again!