During the "Eleventh" holiday, Xiao Ming's family went to go on road trip. Along the way, the kinematics knowledge they learned helped him solve many practical problems. (1) once down,

(1) "Shangqiao 18km" means there is still 18km from this signboard to Shangqiao.

"40" means that the speed of the car cannot exceed 40 km/h;

(2)∫v = ST

∴ At least the time required to reach the bridge from this sign:

t = SV = 18km 40k m/h = 0.45h = 27min；

(3)∫v = ST

The slowest walking time is tslow = s ′ vlow =180km 60km/h = 3h;

The fastest walking time t = s'v height =180km120km/h =1.5h;

Now the time is 10: 00 am, so Xiaoming told his father that the time is11:30 ~13: 00.

Answer: (1) There is still 18km from the signboard to the upper bridge, and the speed cannot exceed 40km/h;

(2) It takes at least 27 minutes; Get to the bridge from the place where the signboard is located;

(3) Xiaoming told his father that the time was11:30 ~13: 00.