A uniform thin rope of length $12 \mathrm{m}$ and mass $6 \mathrm{kg}$ hangs vertically from a rigid support and a block of mass $2 \mathrm{kg}$ is attached to its free end. A transverse short wave train of wavelength $6 \mathrm{cm}$ is produced at the lower and the rope. What is the wavelength of the wave train (in $\mathrm{cm}$ ) when it reaches the top of the rope?