Every physics answer marked wrong for being off by 3.6 is a rate conversion error. Speed in km/h becomes m/s by dividing by 3.6, but the real skill is knowing why. Drag the slider to see any speed convert live — watch both units update simultaneously.
Divide km/h by 3.6 to get m/s because 1 km = 1000 m and 1 hour = 3600 s. The conversion is 1000/3600 = 1/3.6. This works every time: take your speed in km/h, divide by 3.6, and you have m/s. A car at 72 km/h is moving at 20 m/s. Highway speed of 100 km/h is 27.78 m/s. The method never changes — the units force the arithmetic. Physics exams expect m/s, so convert first, calculate second.
Converting rates means tracking two units simultaneously — change the numerator and denominator separately, then simplify the fraction to get the new rate.