# Homework Help: What equation should I use?

1. Feb 13, 2005

### Azytzeen

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!

2. Feb 13, 2005

### xanthym

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: Feb 13, 2005
3. Feb 13, 2005

### Azytzeen

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

4. Feb 13, 2005

### dextercioby

How did you get 88 (what ???),if you didn't have the value of "c"...?Shouldn't the notation be "µ"...?

Daniel.