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The Car Stopping Distance Logarithmicallyfinnish_translation.jpg

Auton pysähtymismatka logaritmisesti

I dare say this approach is not presented elsewhere. The stopping distance is formed on reaction time and braking distance. A suitable reaction time is considered to be 1 second. This information is calculated in the table below. Values in the table are the average of the braking actions, so in traffic be prepared to the worst result.

S = Braking distance      v = initial speed m/s        μ = friction factor 0.8     g = 9.81 m/s2

S = v2 / (2 x μ x g)

Braking on the Clean and Dry Asphalt

Speed        Reaction time  Braking     Tot.

km/h               m                      m            m                                                                      

  30                8.33                  4.42        12.8            Known data 13 m

  40               11.1                   7.9          19.0             40/(Ln pii)6 =   17.8 m

  50               13.9                 12.3          26.2             50/(Ln pii)5 =   25.5 m  

  63               17.5                 19.5          37.0             63/(Ln pii)4 =   37 m

  80               22.2                 31.4          53.6             80/(Ln pii)3 =   53.3 m

100               27.8                 49.2          77.0           100/(Ln pii)2 =   76.3 m

120               33.3                 70.6        103.9           120/(Ln pii)  =  104.8 m

125               34.7                 76.6        111.3           125/(Ln pii)  =  109.2 m

An Example

Known data is ab. 13 m braking distance at speed 30 km/h. What has been the speed of the car, which has left 71 m braking skidmarks?

 30 / x = (13/71)2

 (132) x = (712) * 30

 169 x = 330750

  x=330750/169

  x= 130 km/h

Tarkistus - Check

  S = 36.112 /(2 x 0.8 x 9.81) m                              (130 km/h = 36.11 m/s)

  S = 83 m

Based on the table, the vehicle speed has been 120 to 130 km/h. On the motorway the vehicle has beeen within the limits. The more detailed information cannot determine of the braking skidmarks.

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3.2.2015*23:35 (1008 - 1002)
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