72 km / h = > 72000m/3600s = 20 m/s
Ecuatia lui Galilei : v^2 = v0^2 + 2a( x – x0)
v0 = 0
x0 = 0
x = d
v^2 = 2ad
din aceasta relatie exprimam a (accelaratia)
a = v^2/2d = 20^2 / 2 x 600 = 400/ 1200 = 1/3 m/s^2
t = v/a = 20m/s / 1/3m/s^2 = 20 x 3 s = 60 sec (e)