What is the primary physical reason why a heavy commercial truck requires a significantly longer following distance than a passenger car?

1. The massive gross mass of a heavy truck generates tremendous kinetic energy ($E_k = \frac{1}{2}mv^2$), requiring greater braking force and distance to stop
2. Heavy truck diesel engines consume more air pressure during braking maneuvers
3. Commercial truck tires have lower friction coefficients than bicycle tires on dry concrete
4. Heavy trucks are legally required to stop only using auxiliary exhaust brakes