How can i find the coefficient of kinetic friction?

Click For Summary
SUMMARY

The discussion centers on calculating the coefficient of kinetic friction (μk) for a crate sliding down a ramp inclined at 16 degrees. The user initially calculated the static friction coefficient (μs) as 0.287 using the formula μs = tan(16°). To find μk, the user must determine acceleration (a) without knowing the mass of the crate. The conversation emphasizes the importance of using free body diagrams and the relationship between forces and acceleration in frictional problems.

PREREQUISITES
  • Understanding of Newton's laws of motion
  • Knowledge of free body diagrams (FBD)
  • Familiarity with kinematic equations
  • Basic trigonometry, particularly tangent functions
NEXT STEPS
  • Learn how to derive the coefficient of kinetic friction from acceleration and gravitational forces
  • Study the application of free body diagrams in friction problems
  • Review kinematic equations and their application in solving motion problems
  • Explore the relationship between mass, acceleration, and friction in physics
USEFUL FOR

Students studying physics, particularly those focusing on mechanics, as well as educators seeking to clarify concepts related to friction and motion.

ciara0682
Messages
9
Reaction score
0

Homework Statement



I know incline is 16 degrees
I know distance traveled is 2.85 meters
I know Vf is 2.71 meters/second I calculated the meu static and got .287

Homework Equations

The Attempt at a Solution


Tried every thing so lost
 
Physics news on Phys.org
ciara0682 said:

Homework Statement



I know incline is 16 degrees
I know distance traveled is 2.85 meters
I know Vf is 2.71 meters/secondI calculated the meu static and got .287

Homework Equations

The Attempt at a Solution


Tried every thing so lost

Welcome to the PF.

Please fill out the Template a bit more. What is the exact problem statement? What are the relevant equations? Please show us your work where you say you got the static μ to be 0.287
 
A flatbed truck slowly tilts its bed upwards to dispose of a crate. When the tilt angle is 16 degrees or above the create begins to slide. When the create reaches the bottom of the flatbed, it has slide 2.85 meters, its speed is 2.71 m/s.
I found meu static by summing the forces in both the x and y direction which all and all gave me the formula of meu static = tan of the angle. Tan(16)=.287 now I'm stuck on how to calculate meu kinetic because you need acceleration. But with no mass...I have two variables. I'm just very confused.
 
ciara0682 said:
But with no mass...I have two variables.
Give it a try anyway. Sometimes (when the net force is proportional to the mass) you don't need to know the mass. For example, if I drop my computer right now, even though I have no idea what it's mass is, I can tell you it accelerates at 9.8 m/s/s
 
But in the formula I reach...the masses just can't cancel? I'm sorry, I'm not quite understanding. I get your analogy, but still confused on how it pertains to a frictional problem.
 
ciara0682 said:
A flatbed truck slowly tilts its bed upwards to dispose of a crate. When the tilt angle is 16 degrees or above the create begins to slide. When the create reaches the bottom of the flatbed, it has slide 2.85 meters, its speed is 2.71 m/s.
I found meu static by summing the forces in both the x and y direction which all and all gave me the formula of meu static = tan of the angle. Tan(16)=.287 now I'm stuck on how to calculate meu kinetic because you need acceleration. But with no mass...I have two variables. I'm just very confused.

ciara0682 said:
But in the formula I reach...the masses just can't cancel? I'm sorry, I'm not quite understanding. I get your analogy, but still confused on how it pertains to a frictional problem.

Draw a free body diagram (FBD) for the crate sliding down the ramp. Show the component forces due to gravity and due to the sliding friction. Then use F=ma and sum the forces... Please show that work...
 
I went back to the basics and started with the kinetic formula. Xf=x+volt+1/2at^2... I used Vf=Vo+at solved for t...plugged that into kinematic equation.
Now I have Xf=1/2a(Vf/a) ^2 solved for a. Then plugged that into...meu k(mgcos(theta))-(mgsin(theta))=ma but I have two variables. This is where I'm lost. And who knows of I am even doing that part right.
 
ciara0682 said:
But in the formula I reach...the masses just can't cancel?
Have you actually tried it, or are you just guessing?

ciara0682 said:
I get your analogy, but still confused on how it pertains to a frictional problem.
The analogy was not really supposed to give you any insight; the point of my post was to just try finding μk and see what happens!

If μk depends on mass like you assume it does, then you should at least determine exactly how it depends on mass.
 
I provided you with the work above that I have done so far.
 
  • #10
ciara0682 said:
meu k(mgcos(theta))-(mgsin(theta))=ma but I have two variables.
What happens if you divide both sides by m?
 
  • #11
μk=a/g(cos(theta))-(sin(theta)) ?
 
  • #12
ciara0682 said:
μk=a/g(cos(theta))-(sin(theta)) ?
Double check your algebra. If you get the same answer show your steps.
 
  • #13
μk=a/(gsintheta)-(gcostheta)...I solved for uk and I still got the incorrect answer. grrrrrrrrrr. sorry for growling.
 
  • #14
ciara0682 said:
μk=a/(gsintheta)-(gcostheta)
Your algebra is still wrong. Triple check it :smile:

ciara0682 said:
grrrrrrrrrr. sorry for growling.
As long as you don't bite we're okay.
 
  • #15
a+gsin(theta)/gcos(theta) ...
 
  • #16
From your equation, I get \mu_k=\frac{a}{g\cos\theta}+\tan\theta

Also when you plug in the value for a, remember which directions you chose to be positive and negative (you said that downhill was negative, so the acceleration will be negative)
 
  • #17
trig is not my strongest area. whoops. I realized my mistake in algebra... gracias mi amigo!
 
  • #18
de nada
 
  • Like
Likes   Reactions: ciara0682

Similar threads

Distance travelled by a car considering only air friction?
  • · Replies 4 ·
Replies
4
Views
2K
Does coefficient of kinetic friction depend on speed?
  • · Replies 16 ·
Replies
16
Views
6K
Coefficient of kinetic friction of a block sliding across the ceiling
  • · Replies 7 ·
Replies
7
Views
2K
How do I find the coefficients of static friction and kinetic friction?
  • · Replies 20 ·
Replies
20
Views
3K
How to find the coefficient of kinetic friction
  • · Replies 4 ·
Replies
4
Views
3K
Coefficient of Friction question for a cart going down a wooden ramp
  • · Replies 18 ·
Replies
18
Views
3K
What's the coefficient of kinetic friction?
  • · Replies 8 ·
Replies
8
Views
4K
Minimal rotational kinetic energy for a gyroscope to precess
  • · Replies 33 ·
2
Replies
33
Views
3K
Coefficient of kinetic friction?
  • · Replies 21 ·
Replies
21
Views
2K
Calculating acceleration from the coefficient of kinetic friction
  • · Replies 48 ·
2
Replies
48
Views
8K