A transmission rate of 10 Mbps implies that each bit is sent in 0.1 microseconds. For a coaxial cable, the speed at which the signal travels along the cable is approximately 0.77 times the speed of light (3.0E8 m/s). A bit therefore occupies 23 meters of cable. That means the smallest frame would be 13.3 km long.
For those who no longer use 10-baseT and gave up coax for twisted pair years ago, propagation speed in twisted pair is much slower – roughly 0.59 times the speed of light. I’ll let you do the math for a frame.