Calculate the de Broglie wavelength of a $150\,\text{g}$ ball travelling at $30\,\text{m\,s}^{-1}$. The result tells you why the wave nature of matter is invisible at everyday scales. (Take $h = 6.63\times 10^{-34}\,\text{J\,s}$.)

1. Convert mass to SI: $m = 150\,\text{g} = 0.150\,\text{kg}$. 2. Compute momentum: $p = mv = (0.150)(30) = 4.5\,\text{kg\,m\,s}^{-1}$. 3. Apply $\lambda = h/p$: $\lambda = \dfrac{6.63\times 10^{-34}}{4.5} \approx 1.47\times 10^{-34}\,\text{m}$. 4. Order of magnitude is $10^{-34}\,\text{m}$ — staggeringly smaller than any atomic dimension (an atom is $\sim 10^{-10}\,\text{m}$), let alone anything we can observe. 5. Option D ($10^{-10}\,\text{m}$) is the de Broglie wavelength of an ELECTRON at typical speeds (Example 11.3 part a), not a macroscopic ball. Options A and B are intermediate but wrong by many orders of magnitude. 6. Takeaway: matter wave effects appear only when $\lambda$ is comparable to the size of structures the wave interacts with — easy for electrons, impossible for cricket balls. _Source: NCERT Class 12 Physics Part 2, Ch 11, Example 11.3 (part b), p. 12._