Applying Magnitude Principle to Analyze the Reasonable Maintenance of Auto Stop

When the force acts on the particle, the momentum or velocity of the particle can be changed. The force accumulation effect on time can be expressed by the momentum theorem: the external impulse is equal to the change in momentum. The expression is: F t= mt - m 0 Safety belt protection The relevant data shows that at present, the speed limit of domestic highway vehicles is 100 km h and 120 km h. The car calculates in case of emergency braking and sudden impact. The safety belt provides protection to the occupants. Assume that a high-speed car has a speed of 115 km h (32 ms) and the emergency brake will stop in 2 seconds. If the passenger in the first officer's position is not wearing a seat belt, he is 0.6 m from the windshield (average of average car).

The car starts from the braking deceleration, and the time when the passenger rushes toward the windshield (T) regards the movement of the car from braking to stopping as a straight linear motion. Then the car acceleration: = t - 0 t = 0- 32 2 = - 16 m s2 Assuming that the passenger is not wearing a seatbelt, the seatbelt is not subject to force. At the same time, it can be considered that the friction between the passenger and the seat is negligible, so the movement of the passenger can be approximated as a uniform linear motion.

For example, during the time T, the passenger's travel distance: S 2 = 32 T = S 3 + S 1 = S 3 + 0. 6 (1) The car's distance during T: S 3 = 0 T + 1 2 aT 2 = 32T + 1 2 ( - 16) T 2 (2) solves the two equations (1) and (2) simultaneously: T 0. 27 s The result shows that the car needs to stop in 2 seconds while the passengers are already at 0. 27 seconds has rushed to the windshield.

The passenger was reduced to the same speed as the car at 0. 27 seconds. The force exerted by the seat belt on the passengers (F) allowed the passengers rushing to the windshield to be reduced to the same speed as the car within 0.25 seconds to ensure their safety. To do this, the passenger must be given a force. Assume that the passenger's weight is 65 kg, and the speed of the car after 0. 27 seconds is reduced to: 1 = 0 + aT = 32+ ( - 16) 0. 27 = 27. 68 ms according to the momentum theorem: F t = m 1 - m 0 = 65 (27. 68-32) = F 0. 27 Solution: F = 1 040 N (this corresponds to a weight of 106 kg) The result shows that when the car is braked in an emergency, the passenger must be given a car. With the opposite direction of motion, the size is equivalent to 106 kg of force (this force is provided by the safety belt) to ensure safety.

When the car suddenly hits a stop, the force (F) data provided by the seat belt to the passengers indicates that when the car suddenly hits a rigid object with a velocity of approximately 115 km h, the front of the vehicle is recessed and stops within a few tenths of a second. t = 0. 2 s). To ensure that passengers are parked in their own position with the car.

According to the momentum theorem F t = mt - m 0 = 65 (0-32) = F 0. 2 solution: F 10 400 N (this corresponds to a force of 1 061 kg). The result shows that when a car suddenly hits, people will A greater force (approximately 1 t) impacts the windshield. At this time, the seat belt is required to apply a reverse buffer force to the human to reduce the degree of injury. Therefore, people must wear safety belts while riding.

The data on the protection of airbags indicates that the standard conditions for automotive testing are: a car travelling at a speed of 48 km h (13. 3 ms) after the front has collided with a rigid wall or obstacle (eg, a reinforced concrete wall). The front end is recessed by an average of 0. 7 m. At this time, the safety device of the steering wheel can shorten it by 0.2 m. In the case of whether the car is equipped with an air bag, calculate the impact force that the driver will receive due to the impact of the car.

The time required by the driver's upper body to touch the steering wheel (t) Assume that the car does not have an airbag system and the driver is not wearing a seat belt. His upper body distance steering wheel is 0.36 m (average of average car). The collision motion between the car and the rigid object can still be regarded as uniform linear deceleration. At this time, the driver's movement can still be regarded as uniform linear motion ( Reference 2.1 analysis). The car's acceleration is: a = 2 t - 2 0 2s = 0 2 - 13. 3 2 2 0. 7 = - 126. 35 ms 2 during the time t people's upper body moves Distance: s = 0 t = 13. 3t (1) The distance the steering wheel moves during time t: s = 0 t + 1 2 at 2 = 13. 3t + 1 2 (- 126. 35) t 2 (2) Available Reference was: s = s disk + 0. 36 (3) The above three-way solution was: t = 0. 075 s results show that: when the car and a rigid object impact, the person's upper body after 0. 075 s encounter steering wheel.

The car does not have an airbag system. When the driver hits the steering wheel at a speed of 13.3 ms when the impact is stopped, the driver's upper body generates an impact force. The safety device automatically depresses 0. 2 m. The effect is to increase the distance between the driver and the steering wheel. Buffering effect. If the driver's upper body mass is 30 kg.

In the upper body of the person touched the steering wheel in the distance of 0. 075 s car recess: s = 0 t + 1 2 at 2 = 13. 3 0. 075 + 1 2

(- 126. 35) 0. 075 20. 64 m The distance that the car will continue to sag before stopping is: 0. 7- 0. 64 = 0. 06 m from the person's upper body touches the steering wheel until he finally stops to experience The distance is: 0. 2+ 0. 06= 0. 26 m is the acceleration of the human upper body at this time: a = 2 t - 2 0 2s = 0 2 - 13. 3 2 2 0. 26 = - 340. 2 Ms 2 According to the momentum theorem, the impact force generated by the human upper body: F = mt - 0) t = 30 340. 2 = 10 206 N 188 This corresponds approximately to a force of 1 t.

The results show that if a car does not have a person's airbag, when the car collides with a rigid object, it will impact the steering wheel with a force equivalent to 1 t, resulting in disastrous consequences.

The automobile has an airbag system, and the impact force data generated by the driver's upper body when the impact is stopped indicates that the airbag is installed in the steering wheel of the vehicle. When the vehicle is impacted with the rigid object with an acceleration greater than 100 ms 2 , the airbag is in a strong impact force. Under the effect, the upper cover of the steering wheel would be flushed in an instant of 0.04 s. This creates an air cushion between the driver and the steering wheel. When the driver's body hits the airbag, the internal nitrogen will be discharged from the small hole on the airbag due to the pressure and slowly deflate, thus reducing the impact force.

Within 0. 04 seconds (inflated airbag) the person's upper body forward distance: s = 0 t = 13. 3 0. 04 = 0. 53 m distance in front of the sag in the 0. 04 seconds (body forward Distance) :s car = 0 t+ 1 2 at 2 = 13. 3 0. 04+ 1 2

(- 126. 35) 0. 04 20. 43 m Distance between the person's upper body and the steering wheel: 0. 36- ( 0. 53- 0. 43) = 0. 26 m The car must continue before it completely stops. Depression distance (the distance the body continues to move forward) : 0. 7- 0. 43 = 0. 27 m is the distance from the collision of the upper body of the person to the air bag until it is completely stopped (ignoring the thickness of the air bag after it has completely leaked. ): 0. 26+ 0. 27+ 0. 2= 0. 73 m: The acceleration of the upper body of the person is: a = 2 t - 2 0 2s = 0 2 - 13. 3 2 2 0. 73 = - 121 2 ms 2 According to the momentum theorem: Impact force generated by the human upper body: F = m (t - 0) t = 30 121. 2 = 3 636 N This corresponds to approximately 371 kg of force.

The results show that under the same impact, if the car uses an airbag system, it will impact the steering wheel with a force equivalent to 371 kg. Without the airbag system, people will impact the steering wheel with a force equivalent to 1 t. . Compared with this, the use of an airbag system reduced the impact force by 64% and played a very good protective role.

Conclusion The above analysis shows that the safety belt exerts a force on the person to bind the person to the seat and prevent secondary collision.

The pop-up of the airbag can make people unable to hit the body, both play a buffer role to reduce the degree of harm to people. It should be emphasized that the use of a seat belt is an important condition for the airbag to play a protective role. In general, the effective protection rate is only about 25% with airbags only, the effective protection rate is about 45% 50% with seat belts only, and the effective protection rate with seat belts plus airbags is about 65%. On the one hand, it is necessary to fasten the seat belt and also to use the airbag system.

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