Question

A wave train can travel of 250 km in 1.40 minutes. If the wave train has 4 troughs in 11.0 cm,
then much time (in minutes) does it take the source vibration to create 20.0 million cycles?

Answer 1

$$T=\frac{\lambda}{v}=\frac{0.11(1.4)}{4(250000)}=1.54\cdot10^{-7}min$$

$$t=1.54\cdot10^{-7}(20000000)=3.08\ min$$