You testify as an expert witness in a case involving an accident in which car A slid into the rear of car B, which was stopped at a red ligh

Question

You testify as an expert witness in a case involving an accident in which car A slid into the rear of car B, which was stopped at a red light along a road headed down a hill. You find that the slope of the hill is θ= 12.0°, that the cars were separated by distance d = 24.0 m when the driver of car A put the car into a slide (it lacked any automatic anti-brake-lock system), and that the speed of car A at the onset of braking was Vo= 18.0 m/s.
With what speed did car A hit car B if the coefficient of kinetic friction was (a) 0.60 (dry road surface) and (b) 0.10 (road surface covered with wet leaves)?

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Acacia 4 years 2021-09-01T20:46:50+00:00 1 Answers 11 views 0

Answers ( )

  1. King
    0
    2021-09-01T20:48:21+00:00
    Reply

    Answer:

    Explanation:

    a Downward acceleration of car A along the slope

    = g sinθ – μ g cosθ

    = g ( sinθ – μ  cosθ)

    = 9.8 ( sin 12 – .6 x cos 12 )

    = 9.8 x ( .2079 – .5869 )

    = – 3.714 m / s²

    So there will be deceleration

    v² = u² – 2 a s

    = 18² – 2 x 3.714 x 24

    = 324 – 178

    = 146

    v = 12 .08 m /s

    b )

    In the second case , kinetic friction changes

    downward acceleration

    = g ( sinθ – μ  cosθ)

    = 9.8 ( sin12 – .1 x cos 12 )

    9.8 ( .2079  –  .0978 )

    = 1.079 m /s

    there will be reduced acceleration

    v² = u² – 2 a s

    = 18² +2 x1.079 x 24

    = 324 + 52

    = 376

    v = 19.4  m /s

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