net force on the crates while stopping will be provided by .
the max net force possible would then be
so ... has magnitude
using the "no time" kinematics equation ...
The floor of a railroad flatcar is loaded with loose crates having a coefficient of static friction of 0.40 with the floor. If the train is initially moving at a speed of 52 km/h, in how short a distance can the train be stopped at constant acceleration without causing the crates to slide over the floor?