# Friction Force

1. Oct 10, 2014

### I <3 Physic

1. The problem statement, all variables and given/known data
If a 2.5 kg rubber ball is rolled across the dry concrete floor with an acceleration of 4.0 m/s^2[E]. Determine the friction force required to stop the ball. (Drawing a free body diagram will help illustrate this situation)

2. Relevant equations
Fk= µk(Fn)
F=ma

3. The attempt at a solution

a=4.0 m/s^2[E]

m=2.5kg
µk= 1

Find Fn=mg

=2.5(9.81)

=24.5

Find friction force to stop the ball

Fk=1(24.5)

Fk=24.5

Find Fnet=ma

=2.5(4.0)

=10 N(E)
These numbers are telling me that the object should not be moving in the first place? Which is confusing because i am given an acceleration

2. Oct 10, 2014

### RUber

Why did you set $\mu k = 1$?

3. Oct 10, 2014

### I <3 Physic

that was the value that was given to me, on my coefficients of friction sheet.

4. Oct 10, 2014

### 462chevelle

That is very high, that is a friction i would expect to be static. and i thought rubber to concrete was somewhere around .8 mus