First, note that 100 m = 0.100 km.
Recall that
v² - u² = 2 a ∆x
where u and v are initial and final velocities; a is acceleration; and ∆x is displacement. Solve for a :
(72 km/h)² - (108 km/h)² = 2 a (0.100 km)
a = ((72 km/h)² - (108 km/h)²) / (0.200 km)
a = -32,400 km/h²
If you want to convert this to m/s², we have
(-32,400 km/h²) = (-32,400 km/h²) (1000 m/km) (1/3600 h/s)²
(-32,400 km/h²) = -2.50 m/s²
