v
Solution.
Answer: 20.
Answer: 20
The snowmobile moved in a straight line across the frozen lake at a speed modulus of which Then the engine was turned off. If the coefficient of sliding friction between the runners of the sleigh and the ice then let s, which the snowmobile will pass to a complete stop, is equal to ... m.
Solution.
The modulus of the initial velocity, the modulus of acceleration and the braking distance are related by the relationship: On a horizontal surface, the modulus of acceleration due to the force of friction is Thus,
Answer: 81.
Answer: 81
On a horizontal straight section of a wet asphalt road, the driver of a car moving at a speed whose module applied emergency braking. If the coefficient of sliding friction between the wheels and the asphalt , then the braking distance s, passed by the car to a complete stop, is equal to ... m.
Solution.
The modulus of the initial velocity, the modulus of acceleration and the braking distance are related by the relationship: On a horizontal surface, the modulus of acceleration due to the force of friction is Thus,
Answer: 50.
Answer: 50
On a horizontal straight section of a dry asphalt road, the driver applied emergency braking. The braking distance of the car to a complete stop was . If the coefficient of sliding friction between the wheels and the asphalt, then the speed modulus v 0 car movement at the start stopping distance equals...
Solution.
The modulus of the initial velocity, the modulus of acceleration and the braking distance are related by the relationship: On a horizontal surface, the modulus of acceleration due to the force of friction is Thus,
Answer: 16.
Answer: 16
A car moving at a speed along a straight horizontal section of the road began emergency braking. In the braking distance section, the vehicle speed modulus decreased to If the coefficient of sliding friction between the wheels and the asphalt, then the speed modulus v 0 car movement at the beginning of the braking distance is equal to...
Solution.
The modulus of the initial velocity, the modulus of the final velocity, the modulus of acceleration and the stopping distance are related by the relationship: On a horizontal surface, the modulus of acceleration due to the force of friction is Thus,
Answer: 20.
Answer: 20
t\u003d 1.0 s, and the vehicle acceleration module during braking, then stopping way s
Solution.
moving s
a x= -A.
The full path is
Answer: 63.
Answer: 63
A car is moving along a highway with a speed modulo . Suddenly, an elk ran into the road. If the reaction time of the driver t\u003d 0.80 s, and the vehicle acceleration module during braking, then the stopping distance s(from the moment an obstacle occurs to a complete stop) is ... m.
Solution.
From the moment the moose appeared and until the start of braking, the car went a long way.
moving s 2 vehicles after the start of braking and before stopping:
Projection of acceleration on the direction of motion a x= -A.
The full path is
Answer: 66.
Answer: 66
A car is moving along a highway with a speed modulo . Suddenly, an elk ran into the road. If the reaction time of the driver t s(from the moment an obstacle occurs to a complete stop) is ... m.
Solution.
From the moment the moose appeared and until the start of braking, the car went a long way.
moving s 2 vehicles after the start of braking and before stopping:
Projection of acceleration on the direction of motion a x= -A.
The full path is
Answer: 93.
Answer: 93
A car is moving along a highway with a speed modulo . Suddenly, an elk ran into the road. If the reaction time of the driver t\u003d 0.60 s, and the vehicle acceleration module during braking, then the stopping distance s(from the moment an obstacle occurs to a complete stop) is ... m.
Solution.
From the moment the moose appeared and until the start of braking, the car went a long way.
moving s 2 vehicles after the start of braking and before stopping:
Projection of acceleration on the direction of motion a x= -A.
The full path is
Answer: 28.
Answer: 28
A car is moving along a highway with a speed modulo . Suddenly, an elk ran into the road. If the reaction time of the driver t\u003d 0.95 s, and the vehicle acceleration module during braking, then the stopping distance s(from the moment an obstacle occurs to a complete stop) is ... m.
Solution.
From the moment the moose appeared and until the start of braking, the car went a long way.
moving s 2 vehicles after the start of braking and before stopping:
Projection of acceleration on the direction of motion a x= -A.
The full path is
Answer: 33.
A moving car is acted upon by a number of forces, some of which are directed along the axis of motion of the car, and some - at an angle to this axis. Let us agree to call the first of these forces longitudinal, and the second lateral.
Rice. Scheme of forces acting on driving wheel.
a - a state of immobility; b - state of motion
Longitudinal forces can be directed both in the direction and against the direction of the vehicle. Forces directed in the direction of motion are moving and tend to continue moving. Forces directed against the course of movement are resistance forces and tend to stop the car.
The following longitudinal forces act on a car moving along a horizontal and straight section of the road:
- tractive force
- air resistance force
- rolling resistance force
When the car moves uphill, there is a force of resistance to lifting, and when the car is accelerating, the force of resistance to acceleration (inertia force).
Traction force
The torque developed by the car's engine is transmitted to the drive wheels. Transmission mechanisms are involved in the transmission of torque from the engine to the drive wheels. The torque on the drive wheels depends on the engine torque and gear ratios of the gearbox and main gear. At the point where the wheels touch the road surface, the torque causes a circumferential force. The resistance of the road to this circumferential force is expressed by the reactive force transmitted from the road to the drive wheel. This force is directed towards the movement of the car and is called pushing or traction force. Traction force from the wheels is transferred to the drive axle and then to the frame, making the car move. The magnitude of the traction force is greater, the greater the engine torque and gear ratios gearboxes and final drive. The traction force on the driving wheels reaches largest when the car is moving in a low gear, therefore, a low gear is used when starting a car with a load, when driving a car off-road. The amount of traction force on the driving wheels of the car is limited by the adhesion of the tires to the road surface.
The grip force of the wheels with the road
The friction that occurs between the drive wheels of a car and the road is called traction. The adhesion force is equal to the product of the adhesion coefficient by grip weight, i.e., the weight on the driving wheels of the car. The value of the coefficient of adhesion of tires to the road depends on the quality and condition pavement, the shape and condition of the tire tread pattern, the air pressure in the tire.
In passenger cars, the total weight is distributed approximately equally over the axles. Therefore, its adhesive weight can be taken equal to 50% of the total weight. For trucks at full load, the coupling weight (weight per rear axle) is approximately 60-70% of the total weight.
The value of the coefficient of adhesion is of great importance for the operation of the car and traffic safety, since the vehicle's cross-country ability, braking qualities, the possibility of slipping and skidding of the drive wheels depend on it. With an insignificant coefficient of adhesion, starting the car from a place is accompanied by slipping, and braking is accompanied by slipping of the wheels. As a result, the car sometimes fails to move, and when braking, there is a sharp increase in the braking distance and the occurrence of skidding.
On asphalt pavements in hot weather, bitumen comes to the surface, making the road oily and more slippery, which reduces the coefficient of adhesion. The coefficient of adhesion is especially strongly reduced when the road is wetted by the first rain, when a film of liquid mud that has not yet been washed away is formed. A snowy or icy road is especially dangerous in warm weather when the surface thaws.
With an increase in the speed of movement, the coefficient of adhesion decreases, especially by wet road, since the protrusions of the tire tread pattern do not have time to push through the moisture film.
A good tread pattern of a tire is of great importance when driving on dirt roads, snow, sand, as well as on paved roads covered with a film of mud or water. Due to the projections in the pattern, the bearing area is reduced and consequently the specific pressure on the road surface is increased. At the same time, the mud film is more easily pressed through and contact with the road surface is restored, and on light soil, the projections of the pattern are directly engaged with the ground.
The increased air pressure in the tire reduces its bearing surface, as a result of which the specific pressure increases so much that when starting off and during braking, rubber can be destroyed and the grip of the wheels with the road is reduced.
Thus, the value of the friction coefficient depends on many conditions and can vary within fairly significant limits. Since many traffic accidents are due to bad clutch, then drivers should be able to approximately estimate the value of the friction coefficient and choose the speed and control methods in accordance with it.
Force of air resistance
When driving, the car overcomes air resistance, which consists of several resistances:
- drag (about 55-60% of all air resistance)
- created by the protruding parts-steps of a bus or car, wings (12-18%)
- generated by the passage of air through the radiator and engine compartment(10-15%), etc.
The front of the car compresses and expands the air, while the rear of the car creates a vacuum that causes turbulence.
The force of air resistance depends on the size of the frontal, the surface of the car, its shape, and also on the speed of movement. The frontal area of a truck is defined as the product of the track (distance between tires) and the height of the vehicle. The force of air resistance increases in proportion to the square of the speed of the car (if the speed increases by 2 times, then the air resistance increases by 4 times).
To improve streamlining and reduce air resistance windshield the car is inclined, and the protruding parts (headlights, fenders, door handles) are installed flush with the external outlines of the body. For trucks, you can reduce the force of air resistance by covering the loading platform with a tarpaulin stretched between the cab roof and the tailgate.
Rolling resistance force
A vertical load is constantly applied to each wheel of the car, which causes a vertical reaction of the road. When the vehicle is moving, it is subjected to the rolling resistance force, which occurs due to the deformation of the tires and the road and the friction of the tires on the road.
The rolling resistance force is equal to the product of the gross vehicle weight and the tire rolling resistance coefficient, which depends on the air pressure in the tires and the quality of the road surface. Here are some tire rolling resistance values:
- for asphalt concrete pavement - 0.014-0.020
- for gravel coating-0.02-0.025
- for sand-0.1-0.3
Lift resistance force
The road consists of alternating ascents and descents and rarely has horizontal sections of great length.
When driving uphill, the car experiences additional resistance, which depends on the angle of the road to the horizon. The resistance to lifting is greater, the greater the weight of the car and the angle of inclination of the road. When approaching an incline, it is necessary to correctly assess the possibility of overcoming the incline. If the rise is short, it is overcome with acceleration of the car before lifting. If the rise is long, it is overcome in a lower gear, switching to it at the beginning of the rise.
When the car is moving downhill, the force of resistance to lifting is directed in the direction of movement and is the driving force.
Overclocking resistance force
Part of the traction force during acceleration is spent on accelerating the rotating masses, mainly the flywheel crankshaft car engine and wheels. In order for a car to start moving at a certain speed, it needs to overcome an acceleration resistance force equal to the product of the car's mass and acceleration. When the car accelerates, the acceleration resistance force is directed in the direction opposite to the movement. When braking the car and slowing down its movement, this force is directed towards the movement of the car. There are times when, during a sharp acceleration, cargo or passengers fall from the open, from the motorcycle seats, and when hard braking passengers bump into Windshield or on the front side of the car. In order to avoid such cases, it is necessary, by smoothly increasing the engine crankshaft speed, to overcome the force of resistance to acceleration and smoothly brake the car.
Center of gravity
A car, like any other body, is subject to the force of gravity directed vertically downwards. The center of gravity of a vehicle is the point at which the vehicle's weight is distributed evenly in all directions. In a car, the center of gravity is located between the front and rear axles at a height of about 0.6 m for cars and 0.7-1.0 m for trucks. The lower the center of gravity, the more stable the vehicle is against rollover. When the car is loaded with cargo, the center of gravity rises at cars by about 0.3-0.4 m, and for trucks by 0.5 m or more, depending on the type of cargo. If the load is unevenly stowed, the center of gravity may also shift forward, backward or to the side, which will affect the vehicle's stability and ease of control.
Introduction
The main causes of most accidents and accidents are: poor training of drivers, their unreasonable use of the speed characteristics of the car, non-compliance with safety measures when driving in the city, inept use of the brakes, errors in maneuvering during a skid, violation of the rules of overtaking, passing intersections, railway crossings, non-observance of the distance, incorrect actions when blinded by the light of oncoming traffic.
Statistics show that 60-70% of traffic accidents are caused by incorrect actions (mistakes) of the driver as an element of the driver-car-road system, 20-30% are due to unsatisfactory road conditions and 10-15% - deviations in technical condition car, i.e. the weakest and most unreliable link in this system is the driver. The reliability of the driver is largely determined by the level of his training and professional skills.
One of the main components of driver training is teaching them right action in extreme traffic situations
The movement of cars on dirt road
A dirt road is a road whose canvas is not reinforced by anything and consists of natural soil. If the dirt road bed is reinforced with some kind of durable material (sand, gravel, etc.), then it is called an improved dirt road.
Practice shows that you can easily drive a car on any dirt road, with the exception of sandy.
Dry deep layer sand provides great resistance to the movement of the car and does not provide required grip wheels with the road. The passage of sandy sections of the road in a wet state is improved.
Clay behaves differently when moistened. It becomes plastic, which leads to the formation of a rut, consequently, to an increase in the rolling resistance of the wheels and, at the same time, to a sharp decrease in the force of their adhesion to the road.
Chernozem, like clay, becomes impassable for cars when wet.
In spring and autumn, the carriageway of dirt roads is often destroyed by water. In low places potholes, potholes, deep ruts filled with water are formed.
Roast summer time appears on a dry dirt road a large number of dust that, when rising, impairs visibility.
For successful driving a car on a dirt road, it is important to be able to choose the right direction and speed of movement, provide the necessary traction force, and also timely apply various techniques and devices to increase patency, in order to successfully overcome difficult sections of the road, you should quickly switch to a lower gear. Delayed shifting leads to loss of speed and vehicle stall.
So, during the period of thaw, you need to choose for the passage of such soil, which is less susceptible to the influence of moisture, soaked shallowly.
Difficult sections of the road, when they are short, smooth, with soft ground, it is advisable to overcome with acceleration, using the inertia of the car.
On soft ground, but not on a swampy area, it is better to follow the trail of the car in front. It is possible to drive along the rut when it is not too deep. Otherwise, it is recommended to skip it between the wheels. If the wheels got into a deep rut and it is not possible to get the car out, you should stop it, clear the roadbed under the driving wheels, put branches, boards under them if necessary and leave the rut.
Great difficulties arise when driving on a wet clay road, because wet clay sticks to the wheels, closes the tread lugs, and significantly reduces the adhesion of the wheels to the road. As a result, the drive wheels skid or skid, creating the danger of the vehicle slipping off the road into a ditch. Wet clay areas are best avoided. If this cannot be done, then it is necessary to enable in advance downshift and move with low speed without stopping, braking and sharp turns. In order not to move into a ditch, it is preferable to direct the wheels along the trail of a previously passing car. In particularly difficult areas, you need to use improvised materials. Wheel slippage should not be allowed for a long time.
In the event of a car getting stuck - for example, in a ditch - you can try to get it out using the buildup, which is done by quickly shifting the gears of the front and reversing: forward-backward, forward-backward. With a slight movement of the car forward and backward, the angles of elevation decrease, and some inertia of movement occurs. If this method fails to get the car out, then you need to cut off the edges of the ditch or ditch with a shovel, make them more gentle and, if necessary, place improvised material under the drive wheels or use another car for traction.
When driving on a dirt road with many slopes and steep climbs, it is better to go around uphills, remembering that a detour on a good road, even if it is a long road, is always more economical than driving on a short but bad road.
