Stopping at a Red Light You are driving a 2500.0-kg car at a constant speed of 1

Question

Stopping at a Red Light You are driving a 2500.0-kg car at a constant speed of 14.0 m/s along a wet, but straight, level road. As you approach an intersection, the traffic light turns red. You slam on the brakes. The car's wheels lock, the tires begin skidding, and the car slides to a halt in a distance of 25.0 m. What is the coefficient of kinetic friction between your tires and the wet road? An object in equilibrium has three forces exerted on it A 33.0-N force at 90.0 degree from the x-axis and

Explanation / Answer

distance travelled while braking = S = 25 m

initial velocity = u = 14 m/s

final velicity = v = 0

so we can use kinematic equation

V2-U2 = 2*a*S to find deacceleration

02 - 142= 2*a * 25

=>a = - 3.92 m/s2

now force acting on car = m*a ..............(1)

but this force is due to kinetic friction which is given by ,

frictional force = mu* N = mu* m* g ....................(2)

where

mu= kinetic friction

N= normal reaction

g = acceleration due to gravity

so ,

equating (1) AND (2)

we have,

mu*m* g = m*a

=> mu = a/ g

= 3.92 / 9.8

=0.4

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