# Homework Help: Kinetic Friction and Velocity

1. Oct 4, 2008

### ayreia

1. The problem statement, all variables and given/known data

An 81-kg baseball player slides into second base. The coefficient of kinetic friction between the player and the ground is 0.49. (a) What is the magnitude of the frictional force? (b) If the player comes to rest after 1.6 s, what was his initial velocity?

2. Relevant equations

F = ma, Vo = Vf - at

3. The attempt at a solution

I already got 389 N for (a), now I'm just stuck on (b). Since I have his mass, Vf, and time, all I need is his acceleration to find Vo. I think I have to use F = ma, but I have no idea how to find the horizontal FNET. Ff is 389 N, but since I don't have his forward force, I don't know where to go from here. Thanks for the help!

2. Oct 4, 2008

### G01

What makes you think there is a force on him other than the friction force?

3. Oct 4, 2008

### ayreia

Oh, so, since he's coming to a stop, there's only a frictional force?