# Homework Help: Determining Coefficient of Kinetic Friction w/m, t, and v

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1. Mar 21, 2015

### crushedcorn

1. The problem statement, all variables and given/known data
A 2.0 kg block of wood slides over a horizontal surface and comes to rest in 2.5 s. If its initial velocity was 9.0 m/s, what is the coefficient of kinetic friction?

2. Relevant equations
rho=mv
change in rho=F*change in t
Force of friction = mu*Force normal
Force normal=mg

3. The attempt at a solution
rho=(2.0 kg)(9.0 m/s)=18 kg*m/s
18 kg*m/s=Force of friction(2.5 s)
Force of friction=7.2
mu*Force normal=7.2
mu(2.0 kg)(9.80 m/s squared)=7.2
mu=0.37

I don't know what the correct answer to this question is and I potentially may not know until the day of my exam. Can anyone tell me if I'm doing this correctly or if I'm missing something? I really appreciated it!

2. Mar 21, 2015

### Staff: Mentor

Looks good to me.

F = ma = μN = μmg

a = μg

μ = a/g = [(9m/s)/(2.5s)]/(9.8m/s^2) = 0.367

3. Mar 26, 2015

Thanks!