De - Broglie wavelength associated with a moving ball of mass 0.12 kg and moving a speed of 20 m/s is:

de-Broglie wavelength associated with the an object of mass m moving with velocity v is given by:

$\mathrm{\lambda } = \frac{\mathrm{h}}{\mathrm{mv}}$

de-Broglie wavelength of given ball will be:

$$\begin{gathered} \lambda = \frac{6.626 \times {10}^{-34}}{0.12 \times 20} \\ \Rightarrow \lambda = 2.76 \times {10}^{-34} \mathrm{m} \end{gathered}$$