Coeffincient of static friction

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Homework Help Overview

The discussion revolves around determining the minimum coefficient of static friction required to keep a coffee cup from slipping on a car's dashboard while the car takes a corner. The scenario involves concepts from circular motion and friction.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the formula for the coefficient of static friction and its application to the problem, with some questioning the arithmetic involved in the calculations. There are attempts to clarify the relationship between the forces acting on the cup and the conditions for it to remain stationary.

Discussion Status

Several participants have provided feedback on the calculations, with some suggesting re-evaluation of the values used. Questions about the assumptions regarding the minimum coefficient of static friction and the forces involved have been raised, indicating an ongoing exploration of the problem.

Contextual Notes

Participants are considering the implications of their calculations and the definitions of forces involved, such as centripetal force and normal force, while also addressing potential errors in arithmetic and assumptions about the scenario.

pinkyjoshi65
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Kim has her coffee cup on her car's dash when she takes a corner with radius 4m and 20km/hr. What is the minimum coefficient of static friction which would aloow the coffee cup to stay there without slipping?

this is what i did, but i think it is wrong

MU= friction force/normal force= ma/mg= a/g= v^2/rg
so mu= v^2/rg= 30.80/16*9.8=0.19
 
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pinkyjoshi65 said:
MU= friction force/normal force= ma/mg= a/g= v^2/rg
so mu= v^2/rg= 30.80/16*9.8=0.19
You equation is correct but your arithmetic is not. Did you square the r by mistake?
 
so mu should be = v^2/rg= 30.80/4*9.8=0.78
that is the minimum coefficient of satic friction which would allow the cup to stay in postition without slipping?
 
Yep. (If you're dealing with one of those online systems, you may want to double check the accuracy of your calculations lest you be off a bit. Redo v^2.)
 
how do you know that it is the minimum mu and tht it will make the cup stay in position?
 
Answer these questions:
(1) How much force is required to centripetally accelerate the cup?
(2) What normal force does the cup exert on the surface of the dash?
(3) What's the maximum force that static friction can supply for a given mu?

That should tell you the minimum mu required.
 

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