How Do You Calculate Initial Velocity with Kinetic Friction?

[ayreia]

Homework Statement

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?

Homework Equations

F = ma, V_o = V_f - at

The Attempt at a Solution

I already got 389 N for (a), now I'm just stuck on (b). Since I have his mass, V_f, and time, all I need is his acceleration to find V_o. I think I have to use F = ma, but I have no idea how to find the horizontal F_NET. F_f 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!

 

[G01]

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

 

[ayreia]

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