Coefficent of friction for a box moving at cosntant speed

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Homework Help Overview

The discussion revolves around determining the coefficient of friction for a box being pulled across a horizontal surface at a constant speed, given a specific applied force and mass of the box.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the relationship between the applied force and the force of kinetic friction, questioning the implications of the box moving at constant speed and the resulting acceleration.

Discussion Status

Participants are actively exploring the implications of constant speed on the forces involved, with some noting that the acceleration is zero and discussing the equality of forces. Guidance has been provided regarding the relationship between the applied force and frictional force.

Contextual Notes

There is a focus on understanding the definitions and relationships between the forces involved, particularly regarding kinetic friction and the normal force, as well as the implications of the problem's conditions.

jwxie
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Homework Statement


A horizontal force fo 190N is needed to pull a 70kg box across a horizontal floor at a constant speed. What is the coefficient of friction between the box and the floor?


Homework Equations



Fnet = ma

The Attempt at a Solution



My setup is F - F_f = m*a

But I have trouble getting the acceleration...
F_f is supposed to be F_f = N * u

I am guessing F_f is knifectic fricition? Is it 190N?

I am confused. Please help!
 
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jwxie said:

Homework Statement


A horizontal force fo 190N is needed to pull a 70kg box across a horizontal floor at a constant speed. What is the coefficient of friction between the box and the floor?


Homework Equations



Fnet = ma

The Attempt at a Solution



My setup is F - F_f = m*a

But I have trouble getting the acceleration...
F_f is supposed to be F_f = N * u

I am guessing F_f is knifectic fricition? Is it 190N?

I am confused. Please help!

Yes, Ff is the force of kinetic friction. Notice that the problem says that the box moves at a constant speed. So, what is the acceleration, then? Based on that, and Newton's Second Law (which you've written above), what must be true about how Ff compares to F (the applied force)?
 
a = 0? so it means they are the same force??

So it means all we need is to use the Ff equation now.
 
jwxie said:
a = 0? so it means they are the same force??

So it means all we need is to use the Ff equation now.

Yes, a = 0, so the forces must be the same in magnitude. (They have opposite directions, so they cancel each other out).

Yeah, so since you know the value of Ff, and you know N, you can solve for μ
 

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