# Homework Help: Coefficient of Friction of object sliding down ramp need help

1. Feb 8, 2010

### grr_physics

Coefficient of Friction of object sliding down ramp.. need help!!

1. The problem statement, all variables and given/known data
An 10.0kg object slides down an inclined plane that is 10.0m in length. THe height of the incline is 6.0m and the speed of the object at the bottom is 9.0 m/s.
What is the coefficient of friction of this incline?
So far I found:
Energy lost due to friction= 183.6 J
Force of friction= 18 N

Can someone show me how to find the coefficient of friction ASAP please? This is an advance question in my class for bonus marks & I NEED those bonus marks.

2. Feb 8, 2010

### grr_physics

1. The problem statement, all variables and given/known data
An 10.0kg object slides down an inclined plane that is 10.0m in length. THe height of the incline is 6.0m and the speed of the object at the bottom is 9.0 m/s.
What is the coefficient of friction of this incline?
So far I found:
Energy lost due to friction= 183.6 J
Force of friction= 18 N

Can someone show me how to find the coefficient of friction ASAP please? This is an advance question in my class for bonus marks & I NEED those bonus marks.

3. Feb 8, 2010

### grr_physics

oh yeah i also found the angle at the bottom is 36.869... degrees if that helps.

4. Feb 8, 2010

### grr_physics

Re: Coefficient of Friction of object sliding down ramp.. need help!!

oh yeah i also found the angle at the bottom is 36.869... degrees if that helps

5. Feb 8, 2010

### w3390

The formula relating friction force and coefficient of friction is: f = u*Fn, where f is the friction force, u is mu(coefficient of friction), and Fn is the normal force.

6. Feb 8, 2010

### grr_physics

how do I find the normal force?
I just started physics 30 & totally forget everything... :(

7. Feb 8, 2010

### PhanthomJay

Re: Coefficient of Friction of object sliding down ramp.. need help!!

You have the friction force, so now what formula relates the friction force with the coeff. of friction??

8. Feb 8, 2010

### grr_physics

Re: Coefficient of Friction of object sliding down ramp.. need help!!

u= F/ Fn but i don't know what my Fn is?

9. Feb 8, 2010

### grr_physics

Re: Coefficient of Friction of object sliding down ramp.. need help!!

okay i did tried this:

Fn= (10.0kg)(cos(36.869...degrees))(9.81)
= 78.48...N

u=F/Fn
=0.22935...

is this correct?

10. Feb 8, 2010

### w3390

the normal force is the force the object exerts on whatever surface it rests. In other words, its mass(i.e. m*g)

11. Feb 8, 2010

### PhanthomJay

Re: Coefficient of Friction of object sliding down ramp.. need help!!

Ok, Fn is the normal force acting on the object perpendicular to the incline. Call that direction the 'y' axis, and the direction along the incline will be the 'x' axis. In the y direction, there is no acceleration, so Newton's first law applies. Identify all the forces or force components in the y direction (what are they?) and set their sum equal to 0 to solve for Fn .

12. Feb 8, 2010

### grr_physics

okay i did tried this:

Fn= (10.0kg)(cos(36.869...degrees))(9.81)
= 78.48...N

u=F/Fn
=0.22935...

is this correct?

13. Feb 8, 2010

### grr_physics

Re: Coefficient of Friction of object sliding down ramp.. need help!!

I don't know the other forces, only the top mechanical energy & bottom mechanical energy

14. Feb 8, 2010

### PhanthomJay

Re: Coefficient of Friction of object sliding down ramp.. need help!!

You didn't need the hint, nice job! Just be sure to round off the coefficient to one (or 2 at the most) decimal places.

15. Feb 8, 2010

### PhanthomJay

Re: Coefficient of Friction of object sliding down ramp.. need help!!

Oh, how did you find Fn if you didn't know the other force acting? Did you look it up somewhere?

16. Feb 8, 2010

### grr_physics

Re: Coefficient of Friction of object sliding down ramp.. need help!!

i figured out the 18 N in class but I don't remember how but thanks a bunch for the help, even though u say I didn't need the hint, your hint made me think & brought back everything! =)

17. Feb 8, 2010