Originally Posted by awblain
If you load up the same truck with more weight, keeping the same brakes, then it takes longer to stop.
Not necessarily, it depends on the brakes and the friction available between tires and road surface. That's why I added the caveat 'brakes sufficiently powerful'. The maximum retarding force from a braked, rolling wheel is obtained when one of the following conditions is reached, whichever comes first when increasing the pressure applied to the brakes:
(a) the brake pressure equals the maximum brake pressure, or
(b) the tires start skidding.
In this context 'brakes sufficiently powerful' means that condition (b) applies. The braking force is then proportional to the load on the wheel.