Answer
$k=16 m^{-1}$
Work Step by Step
As we know that $v=\frac{d}{t}$
putting $d=0.060 m$ and $t=0.0040 s$
$v=\frac{0.060}{0.0040}=15\frac{m}{s}$
The angular wave number$k=\frac{2\pi}{\lambda}=$ where $\lambda=0.40 m$
putting the values, we get
$k=\frac{2(3.14)(0.40)}{0.40}=16 m^{-1}$
