# Coefficient Of Static Friction

1. Nov 1, 2008

### kaylanp01

I'm sure that this is a very simple question, but I can't find it in my text. I made a few attempts but I see why they're incorrect, I just can't figure out the correct method.

1. The problem statement, all variables and given/known data
A flatbed truck is carrying a 60.0 kg crate along a level road. The coefficient of static friction between the crate and the bed is 0.490. What is the magnitude of the maximum acceleration that the truck can have if the crate is to stay in place?

2. Relevant equations
I used N-mg=may.

3. The attempt at a solution
N=mg
0.490/60 = 0.008 ( I see why this is incorrect).

and

N=mg=(60)(-9.81)=-588.6 N (I think that I have to use this somehow).

Thanks!

2. Nov 1, 2008

### tiny-tim

Hi kaylanp01!

(have a mu: µ )

Hint: ignore m … the m's all cancel … the acceleration is the same for any object with the same µ.

3. Nov 1, 2008

### kaylanp01

I still don't understand. Do I need to introduce a new formula? Or do I have everything that I need there already?

Thanks for the µ :).

4. Nov 1, 2008

### tiny-tim

Hi kaylanp01!
erm … well, you need a formula involving µ, for a start!

5. Nov 1, 2008

### kaylanp01

haha hey now, be nice. its a saturday night and i'm doing a physics capa, how good is my mindset supposed to be right now? :P

the only formula that I can find with µ is the one for kinetic friction, but i can't see how thats significant. am i missing something?

6. Nov 1, 2008

### tiny-tim

wot's a capa?
mmm … how about an equation relating normal force to static friction?

(or, to put it another way, what is the coefficient of friction?)

7. Nov 1, 2008

### kaylanp01

a capa is hell in the form of an online assignment. haha.

okay, i have the formula that you're talking about, i think...and i assume that it gives you
fs(max)= µsN=0.490(-588.6)=288.4

fs=ma
-288.4=(60)a
a=-4.81 m/s^2=4.81 m/s^2

now i shall insert that answer andddd...
correct!

thank you thank you! :)

8. Nov 1, 2008

### tiny-tim

Woohoo!

… though you would get even more marks if you didn't put those m's in.

9. Nov 1, 2008

### kaylanp01

the sad part about a capa is that every question is only worth 1 mark :(, but i will keep that in mind for my exam :).