All bodies start from rest at the top of the same incline. Which reaches the bottom first?

Acceleration a = g*sin$\frac{theta}{(1 + k^2/R^2)}$. Larger a means faster.

Sliding block (no rotation): $k^2$/$R^2$ = 0, a = g*sin(theta). Always faster than any rolling body.

Critical insight: Mass and radius cancel out. A tiny marble and a huge bowling ball (both solid spheres) reach the bottom at the same time.