This is the boss. No calculator — today $g = 10\ \mathrm{m/s^2}$, the round number every physicist keeps for mental work, and the values are chosen to fit in your head. One crate, one long problem, and every answer feeds the next: weight, then the normal force, then friction's cut, then the net, then Newton, then the speed it all buys. Write each line down as you go — one early slip rolls all the way to the end of the dock.

Everything from the chapter rides in it. 5★ under par here is the chapter crown. Clock in.