1. The problem statement 1) A train whistle has a frequency of 1000 Hz. If the train is speeding at a velocity of 60 km/h past a stationary railroad crossing attendant, what is the apparent frequency a) as the train approaches him, b) as it moves away from him? Assume speed of sound to be 350 m/s. 2) A second train is approaching the first train (above) with a speed of 60 km/h. Obtain the frequency of the whistle of the first as heard by the engineer of the second train. 3) Sound is reflected by a screen moving with a speed 20 km/h toward the source and observer. If the frequency of the source is 450 khz, what is the apparent frequency of the reflected sound? 2. Relevant equations f2 = f1Vs/(Vs + or - Vo), f2 = f1(1 + or - Vo/Vs) meh I'm really not that quite sure :S 3. The attempt at a solution I could calculate number 1 using the doppler effect equation f2 = f1Vs/(Vs + or - Vo), but I'm not quite sure how to solve for number 2 and 3... help please ?