# What equation should I use?

Hello all. I am currently stuck on a problem,

"If the coefficient of kinetic friction between tires and dry pavement is 'c', what is the shortest distance in which an automobile can be stopped by locking the brakes when traveling at 'v'?
Take the free fall acceleration to be g=9.80."

Notice that 'c' and 'v' are blocked out as I am not looking for people to do the problem for me, as said on the sticky. So I was wondering, what kind of equation should I use? Because I could not find one that includes velocity or others without asking for the mass. I tried to derive some, but the answers are all wrong. So please help. Thanks in advance!

xanthym
Azytzeen said:
Hello all. I am currently stuck on a problem,

"If the coefficient of kinetic friction between tires and dry pavement is 'c', what is the shortest distance in which an automobile can be stopped by locking the brakes when traveling at 'v'?
Take the free fall acceleration to be g=9.80."

Notice that 'c' and 'v' are blocked out as I am not looking for people to do the problem for me, as said on the sticky. So I was wondering, what kind of equation should I use? Because I could not find one that includes velocity or others without asking for the mass. I tried to derive some, but the answers are all wrong. So please help. Thanks in advance!

Use conservation of energy. Mass "m" will cancel, then solve for distance "d":
{Delta K.E.} = {Work}
(1/2)mv^2 = c(mg)d
d = (v^2)/(2cg)

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Last edited:
Ohh, I see where my error is now. I kept on getting 88. Thanks for helping me!

dextercioby