The de Broglie wavelength of a tennis ball of mass 60 g moving with a velocity of 10 m  is approximately :

(Plank's constant, $\mathrm{h} = 6.63 \mathrm{x} {10}^{-34} \mathrm{Js}$)

Given that,
Mass of ball $\mathrm{m}=60 \mathrm{g}$
Velocity $\mathrm{v}=10\mathrm{m}/\mathrm{s}$  
Plank constant, $\mathrm{h} = 6.63 \mathrm{x} {10}^{-34} \mathrm{Js}$  

We know that,

$\lambda =\frac{6.63\times {10}^{-34}}{60\times {10}^{-3}\times 10}$

Hence, the wavelength is ${10}^{-33}\mathrm{m}$