The relationship between braking distance s (m) and vehicle speed x (km/h) of a certain type of vehicle on a certain road surface is s= 1/60 x? If the car finds an obstacle 40 meters ahead during driving, what is the maximum speed limit in order to stop at a place not less than 5 meters away from the obstacle? (Suppose it takes 1.5 seconds for the car to stop and find an obstacle. )

Set the maximum speed limit to x km/h.

The car must stop when it leaves the obstacle 40-5=35 (meters).

In addition, within 1.5 seconds, the distance traveled by the car is:1.5×1/3600×××1000 = 5/12x (m).

(The interpretation of this formula is: 1.5 seconds is first passed by × 1/3600, and the unit is converted into "hours"; The distance is obtained by x, time x speed, but because the unit of x is km/h, the distance is obtained in km; Finally × 1000, which can be converted into "meters")

Therefore, 5/ 12x+ 1/60x2=35.

? x2+25x-35×60=0

(x+60)(x-35)=0

So you get x=35.