Question

An old car is traveling down a long, straight, dry road at 25.0 m/s when the driver slams on the brakes, locking the wheels. The car comes to a complete stop after sliding 305 m in a straight line. If the car has a mass of 755 kg, what is the coefficient of kinetic friction between the tires and the road?

vi= 25 m/s
vf=0
x=305

I used vf^2= vi^2+2ax

0=(25^2)+2a(305)

0=625+ 610 a

a=-625/610

a= -1.025 m/(s^2)

mu(k)= a/g

mu(k)= -1.025/9.8

mu(k)= -.1045

I put this in as an answer and it said I was wrong. Can anyone tell me what I'm doing wrong? Or possibly a different way to go about the problem? Help is much appreciated!

Answer 1

You did everything right. You just need to change the sign at the end. so your answer should be +0.1045

Hope this helps :)