Skid marks left by all four wheels of a car on level pavement are measured by a

Question

Skid marks left by all four wheels of a car on level pavement are measured by a police officer to be 20m in length. The driver of the car claims that she was not exceeding the speed limit of 80km/h before she applied the brakes. Furthermore the driver released the brakes before coming to a stop and was observed to continue at a speed of 40km/h after her skid. It is known from prevailing conditions that the coefficient of kinetic friction between the tires and the road was at least 0.80. Can it be shown that the driver was guilty of speeding?

Explanation / Answer

skid marks length =20 meter

so s=20 meter

initial speed for skeed(U) =80km/h=80*1000/3600 =22.22m/s

last speed for skeed (V)=40km/h=11.11m/s

v2-u2=2as

a=22.222-11.112/2*20

= 370.29/40 =9.25m/s2

v=u+at

so t=v-u/a =22.22-11.11/9.25 =1.20 second

a=coefficient of friction* g

so a=.80*9.81 =7.84

which is not equal

so dirver is telling lie and not guilty

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.