Respostas

2014-02-12T11:13:54-02:00
Vm = 72 km/h = 20 m/s
d = 240 m

Vm =  \frac{d}{t} \\\\
20 =  \frac{240}{t} \\\\
t = \frac{240}{20}\\\\
\boxed{t = 12 s}