121). A train whistle (frequency 1800 Hz) is traveling away from an observer at a speed of 16.4 m/s. If the speed of sound is 344 m/s, what is the apparent frequency of the sound as heard by the stationary observer?

4). If a 7.45 kg mass is hung on the end of a vertical spring and it oscillates with a period of 5.42 seconds, what is the spring constant?