m = 775kg
v = 60km/h = 16,66m/s
s = 20m

s = 0.5at^2, v = at
=> s = 0.5a(v/a)^2
=> a = v^2/(2s)

F = ma = 775kg * (16,66m/s)^2 / (2*20m) = 5,382kN.