Question $43$

$2$ pts

A tuning fork has a frequency of $800$ Hz and hence a period of $1\mathrm{.}25{10}^{-3}s.$ If the tuning fork is in an inertial frame of reference moving by the observer at speed of $0\mathrm{.}690c,$ what is the frequency of the fork as measured by the observer? $($Assume that measurements are strictly by optical means and that the speed of sound waves in air is not pertinent here$).$

$579$ Hz

$1110$ Hz

$445$ Hz

$419$ Hz

$1440$ Hz