How to Find Force of Friction and Acceleration?

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Homework Help Overview

The discussion revolves around a physics problem involving a stationary object on a table, where participants are tasked with determining the force of friction and the acceleration of the object when a horizontal force is applied. The problem includes coefficients of static and kinetic friction, as well as the mass of the object.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • The original poster attempts to calculate the force of friction using the coefficient of kinetic friction, expressing confusion about the relevance of static versus kinetic friction. They also attempt to find acceleration using the applied force.
  • Some participants question the necessity of determining whether the object will move before calculating friction, emphasizing the role of the static coefficient in this context.
  • Others suggest that the original poster should clarify their calculations to better understand the relationship between the applied force and the frictional force.

Discussion Status

The discussion is ongoing, with participants exploring the conditions under which the object may or may not move. There is a focus on understanding the application of static and kinetic friction, and guidance has been provided regarding the need to assess the movement of the object before proceeding with calculations.

Contextual Notes

Participants are navigating the implications of the coefficients of friction provided in the problem, and there is an emphasis on the need for clarity in the original poster's calculations and reasoning.

Thomas10
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Homework Statement


Hey, guys I'm having trouble solving this problem, I'm not sure what to do first
This is the info it gives:
A stationary 15 kg object is located on a table near the surface of the earth. The coefficient of static friction between the surfaces is 0.40 and the coefficient of kinetic friction is 0.25.
This is the problem:
A horizontal force of 20 N is applied to the object.
A)Determine the force of friction.
B)Determine the acceleration of the object.

Homework Equations


F=MA
F=uN
W=MG

The Attempt at a Solution


For this part A of this problem I wasn't sure if this was right but what I did was I first found the weight which is 15x9.81=147.15 I then got confused since the problem gives coefficient of static and kinetic since I thought the object was moving I used the formula F=uN and used the coefficient of kinetic friction so .25 times the weigh 147.15 and then I got 36.7875 I'm not sure if this is the right answer for part b to find the force of friction.

For part B of this problem I completely don't know what to do I thought that 20N was a force I can plug in for F=MA so I thought I can divide 20 by 15 which is the weight to find acceleration
 
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When a force is applied to an object that is in resting contact with a surface, the first question is whether it will move relative to the surface. For that you must use the static coefficient. The static coefficient tells you the maximum frictional force available. The actual frictional force will never exceed the net of the other applied forces.
If the static frictional force is insufficient to withstand the net applied force, then the object will move and the frictional force should be calculated using the kinetic coefficient.
 
haruspex said:
When a force is applied to an object that is in resting contact with a surface, the first question is whether it will move relative to the surface. For that you must use the static coefficient. The static coefficient tells you the maximum frictional force available. The actual frictional force will never exceed the net of the other applied forces.
If the static frictional force is insufficient to withstand the net applied force, then the object will move and the frictional force should be calculated using the kinetic coefficient.
I get part A of my problem but now how do I find the acceleration of the object?
 
Thomas10 said:
I get part A of my problem
I don't think you do. If you did, you would be able to answer part B easily.
As I wrote in post #2, your first step must be to determine whether the object moves at all. Please post your working for that.
 

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