Given:
Mass of block = m0
Mass of cylinder = m0
Given that a cylinder is placed at the top of an incline and the block is also placed at the top of a separate rough incline.
Given that both objects reach the bottom of their respective inclines with the same translational speed, let's explain why.
Since the mass of the cylinder and mass of the block are the same, both objects can be said to be rolling down their respective inclines downward along the smooth slope due to the acceleration due to gravity.
In this case the downward acceleration of the cylinder will be higher than that of the block. Although the acceleration of the block should be higher due to the rotational inertia. This happens because the block is exposed to a higher frictional level(due to its rough incline) which causes it to slow down, hence its acceleration will now be apparently the same with that of the cylinder.
In this case, we now have equal initial velocities, equal masses, and equal acceleration.
Since these units are the same, both the block and the cylinder will have reach the bottom of their inclines with the same translational speed.
We have the figure below: