Answer
$f = 1.5\times 10^6~Hz$
Work Step by Step
We can find the frequency required for a good scan.
$f~\lambda = v$
$f = \frac{v}{\lambda}$
$f = \frac{1500~m/s}{1.0\times 10^{-3}~m}$
$f = 1.5\times 10^6~Hz$
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