For the sake of safety, the necessary distance should be kept between the vehicles driving on the highway. It is known that the maximum speed limit of a certain highway is v = 120km / h. assuming that the vehicle in front stops suddenly, the time (reaction time) t between the driver of the rear vehicle and the vehicle starting to decelerate after operating the brake is 0.5s, and the resistance F of the vehicle during braking is 0.4 times of the vehicle gravity, then the high-speed highway will stop What is the minimum distance s between cars on the road?

For the sake of safety, the necessary distance should be kept between the vehicles driving on the highway. It is known that the maximum speed limit of a certain highway is v = 120km / h. assuming that the vehicle in front stops suddenly, the time (reaction time) t between the driver of the rear vehicle and the vehicle starting to decelerate after operating the brake is 0.5s, and the resistance F of the vehicle during braking is 0.4 times of the vehicle gravity, then the high-speed highway will stop What is the minimum distance s between cars on the road?

The initial speed of the car is v = 120km / h = 1003m / S. in the reaction time, the car moves at a constant speed. The distance of motion is S1 = VT = 1003 × 0.5m = 16.67m. When the brake is set, the acceleration of the car is a, and the mass of the car is m. The solution is f = ma = 0.4mg. The solution is a = 4m / S2. From the brake to the stop, the distance of the car is S2 = v22a = (1003) 22 × 4m = 138.9m. The distance s between the cars on the highway should be at least 1 S = S1 + S2 = 16.67 + 138.9m = 155.57m A: the distance s between cars on the expressway should be at least 155.57m

It is known that the maximum speed limit of an expressway is 120km / h. suppose that the vehicle in front stops suddenly and the waiting driver finds this situation from the beginning,
(following the above question) the time (i.e. reaction time) between the operation of the brake and the start of deceleration of the car is 0.5s. The acceleration of the car when braking is 4m / S2. What is the minimum distance s between cars on the highway? (g = 10m / S2)

In this case, the reaction time is uniform motion, and then decelerates to rest
Uniform displacement x = (120 / 3.6) * 0.5 = 50 / 3 M
Deceleration displacement 2ax1 = V ^ 2-0
3*4x1=(120/3.6)^2
x1=92.6m
The total displacement is equal to x + X1 = 126 meters
It has nothing to do with the acceleration of gravity

It is known that the maximum speed limit of a certain expressway is v = 120km / h. suppose that the car in front stops suddenly, and the driver in the rear finds this situation and operates the brake,
The time to start deceleration (i.e. reaction time) t = 0.5s, the acceleration of the car when braking is a = 4m / s * 2, how far should the car room be kept on the highway at least?

The general safe vehicle distance is 200m, d = 1.47si × T + (si2-sf2) / 30 (0.348 ± 0.01g). D is the braking distance, Si is the initial speed, SF is the final speed, t is the reaction time, and G is the slope. This formula is commonly used in the world to calculate the braking distance (British system), The data is 148.3m. This does not take into account the slope, the friction coefficient of the ground and the degree of tire wear (if it is rainy, the ground skids and the driver's reaction time, the actual braking distance is far more than this data)