Q.Calculate the de Broglie wavelength associated with a ball of mass $0.20\ \text{kg}$ moving with a speed of $10\ \text{m/s}$, and comment on why its wave nature is never observed in practice.

Calculation. $\lambda=\frac{h}{mv}=\frac{6.63\times10^{-34}}{0.20\times10}=\frac{6.63\times10^{-34}}{2.0}\approx3.32\times10^{-34}\ \text{m}$

Comment. This wavelength is about $10^{-24}$ times smaller than the diameter of a single atomic nucleus (of order $10^{-15}\ \text{m}$) -- utterly beyond any conceivable means of detection, and with no observable physical consequence for the ball's motion. This is exactly the reasoning behind Exercise 9: the de Broglie wavelength formula applies to the ball just as validly as to an electron, but the ball's enormously larger momentum, compared to Planck's constant …

Apply $\lambda=h/mv$ directly with the given mass and speed, then compare the resulting wavelength with atomi …

• Leaving the answer as a bare number without the physical comment the question explicitly asks for (why the wave nature is never observed). …