Why classical mechanics is unable to explain black body radiation?

Answer 1

Classical mechanics contains the mathematical assumption that everything is infinitely divisible; no matter how small something is, it can always be cut in half. When this idea is applied to calculations of black body radiation the result is what was known as the ultraviolet catastrophe, which is that as the wavelength decreases, the amount of radiation increases without limit, rising asymptotically to infinity. That is, of course, not anything like what we observe in the real world. The solution of quantization, meaning that light (and everything else) just comes in pieces of a certain irreducible size, and no smaller, solves the problem and gives calculations that agree with experimental observations.