# Find coefficient of friction

1. Mar 16, 2012

### menco

1. The problem statement, all variables and given/known data
A truck weighing 15 tonnes is traveling down an decline of 15 degrees at 6.6m in 3s. He then stops and gets out. The truck then begins to roll down the decline as the brakes have failed.

1. What is the size of friction force acting on the rubber tyres of the charging vehicle
2. Coefficient of friction between the rubber tyres and the coal surface.

Knowns/Unknowns
m=15000kg
angle = 15 degrees
d=6.6m
t=3s
g=9.8m/s^2
F(friction) = ?
Coefficient of friction = ?

(I dont think rolling friction is a part of this problem as we have not been taught it yet, but I could be wrong)

2. Relevant equations
Fg = ma
Fg(parallel)= Fg sin (15)
Fg(perpendicular) = Fg cos (15)
Coefficient = F(friction)/ F(normal)

3. The attempt at a solution
1. Fg = 15000 x 9.8 = 147000 N
Fg(parallel) = 147000 sin (15) = 38046.4 N

Therefore F(friction) is 38046.4 N

2. Fg(perpendicular) = 147000 cos (15) = 141991 N = F(normal)
Coefficient = F(friction)/F(normal) = 38046.4/141991 = 0.27

Therefore the coefficient of friction is 0.27.

Am I at least on the right track if I got it wrong?

Last edited: Mar 16, 2012
2. Mar 16, 2012

### tal444

Looks right to me, although I could be wrong.

3. Mar 19, 2012

### menco

Thanks for the response hopefully it is correct. Im just unsure if Im on the right track with Friction force

4. Apr 13, 2012

### menco

solved thanks can someone please delete?

5. Apr 13, 2012

### tal444

We don't delete finished threads. They're kept for anyone who might search up similar questions in the future.