A 2.50-kg Pendulum is attatched to a string 11.4m stringis pulled aside until it is.386m above its lowest position and released. The pendulum is designed to emit sound waves at a frequency of 440 Hz; However, as it swings toward and away from an observer, the frequency appears to vary slightly. What is this Phenomenon called? What would be the apparent frequency of the sound from the pendulum as it swings at its maximum speed toward an observer? Assume the speed of sound is 345 m/s.

Answer 1

The frequency change is called the Doppler shift. Calculate maximum pendulum speed V, which occurs at the bottom of the swing's motion.

Conservation of Energy tells you that

(1/2)V^2 = g * 0.386 m

Solve for V. Then use the Doppler formula for the higher-pitched frequency at maximum velocity V.

The shift is approximately
delta f = fo * (V/345 m/s)
Add that to fo = 440 Hz for the frequency that is heard by a stationary listener

Answer 2

http://en.wikipedia.org/wiki/Christian_Doppler