1. The problem statement, all variables and given/known data The Doppler shift was first tested in 1845 by the French scientist B. Ballot. He had a trumpet player sound an A 440 Hz while riding on a flatcar pulled by a locomotive. At the same time, a stationary trumpeter played the same note. Ballot heard 3.0 beats per second. How fast was the train moving toward him? 2. Relevant equations f' = f/(1-Vs/V) 3. The attempt at a solution Since it said that Ballot heard 3 bps, I added 3 to 440 443 = 440/(1-Vs/V) >> 1-Vs/V = 440/443 >> Vs = (440/443 - 1)-V >> Vs = (440/443 - 1)-343 >> Vs = 2.32 m/s This doesn't seem right to me. I wasn't really sure if I should have added 3 to 440, but I didn't know how else to find the answer.