Question
I do not know how to do this problem at all. The problem reads: You are in charge of an accident reconstruction case for thelocal police department. In oder to determine car speeds,skid mark lengths are measured. To determine the coefficientof kinetic friction, you get into an identical car, and at a speedof 65.2 mi/h, you lock its brakes and skid 51.5 m to rest. (a)Determine the car's deceleration. (b) What is the coefficient ofkinetic friction between the tires and road surface? (c) Thecar in the accident actually skidded 57.3 m. What was its initialspeed? I do not know how to do this problem at all. The problem reads: You are in charge of an accident reconstruction case for thelocal police department. In oder to determine car speeds,skid mark lengths are measured. To determine the coefficientof kinetic friction, you get into an identical car, and at a speedof 65.2 mi/h, you lock its brakes and skid 51.5 m to rest. (a)Determine the car's deceleration. (b) What is the coefficient ofkinetic friction between the tires and road surface? (c) Thecar in the accident actually skidded 57.3 m. What was its initialspeed?
Explanation / Answer
(a) Initial velocity, U = 65.2mi/h = 65.2 ( 1609 / 3600 ) m/s = 29.14 m/s finalvelocity , v = 0 displacement, S = 51.5 m acceleration, a = ( V 2 - U 2 ) / 2 S = -8.24 m/ s^2 deceleration = 8.24 m/s^2 (b) k = a / g = 8.24/ 9.8 = 0.84 (c) displacement, S = 57.3m acceleration,a = - 8.24 m/ s^2 V2 - U2 = 2 a S 0 - U2 = 2 a S - U2 = 2 (- 8.24 ) ( 57.3) U= 30.73 m/s