How to Find Force of Friction and Acceleration?

AI Thread Summary
To find the force of friction and acceleration of a 15 kg object on a table with given coefficients of static and kinetic friction, first determine if the object will move when a 20 N force is applied. The static friction coefficient of 0.40 indicates the maximum frictional force is 58.8 N (0.40 x 147.15 N), which exceeds the applied force, meaning the object does not move. Since the object remains stationary, the force of friction is equal to the applied force of 20 N. To find acceleration, since the object does not move, it remains at zero acceleration. Understanding the distinction between static and kinetic friction is crucial in solving these types of problems.
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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