Suppose a stationary bat emits sound wave with a frequency of $49\mathrm{.}0\mathrm{????}\mathrm{????}\mathrm{With}($note: kilohertz$).$ A beetle flies away from it at $27\mathrm{.}5\frac{\mathrm{????}}{\mathrm{????}}.$ What frequency of reflected sound does the bat hear? Be careful. The beetle behaves like a moving observer and "hears" a frequency different from $49\mathrm{.}0\mathrm{????}\mathrm{????}\mathrm{With}.$ The sound bounces off the beetle and goes back toward the bat. At this point the beetle is acting like a moving source of sound at the frequency the beetle hears.