Answer:
1.3804313 * 10^(-35) m
Step-by-step explanation:
de Broglie's wavelength (λ) = h/p
= h/mv
Firstly, the momentum of the ball would be mass (0.4 kg) * velocity (120 m/s) = 48 g m/s
Now, h = 6.62607 * 10^(-34) Js
Plug in the values now:
λ = 6.62607 * 10^(-34)/48
= 1.3804313 * 10^(-35) m