# Homework Help: What is the magnitude of the frictional force?

1. Mar 25, 2009

### soul5

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

A person pushes with force of 220N on a 40 kg create. The coefficent of kinetic friction of 0.35. What is the magnitude of the frictional force?

2. Relevant equations

Ff = uN

3. The attempt at a solution

so do I just go

Ff = 0.35*(40kg)(9.81m/s^2)

Is that it?

What is the 220 Force for?

2. Mar 25, 2009

### LowlyPion

Re: Friction

As stated it seems to be. But what if the force had been just 100N? The frictional force would only have been 100N then wouldn't it? The point is that the crate is being pushed with sufficient force to involve kinetic friction.

Now if the force is not strictly horizontal, then there is the additional normal component that would also need to be taken into account to determine the frictional force.

3. Mar 25, 2009

### Dr.D

Re: Friction

What direction is the 200 N applied to the crate?

4. Mar 25, 2009

### soul5

Re: Friction

strictly horizontal why do you ask?

5. Mar 25, 2009

### LowlyPion

Re: Friction

Any angle would mean that there would be an additional normal force that would need to be accounted for. It would be the normal component of the force that would then be added to its weight and multiplied by μ.