Moving a block with kinetic and static friction to find the net force?

In summary, the coefficient of static friction is 0.37, the coefficient of kinetic friction is 0.14, and the mass of the block is 3.4 kg. The net force on the block the instant it starts to slide is the difference between the static friction force and the kinetic friction force, which is equal to μs*m*g - μk*m*g.
  • #1
disque
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0
The coefficient of static friction between a block and a horizontal floor is 0.37, while the coefficient of kinetic friction is 0.14. The mass of the block is 3.4 kg. If a horizontal force is slowly increased until it is barely enough to make the block start moving, what is the net force on the block the instant that it starts to slide?

I tried multiple ways of solving this problem, but am only down to one attempt left for credit on my homework. I don't know if I'm over analyzing the problem or what, but its giving me trouble, please help. Thank you
 
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  • #2
What force is required to move the block? Or more specifically what is the greatest amount of resistance the static friction can provide?

μs*m*g

But that's the static friction. But that is the first part of what you want.

After it moves then it is opposed by the μk*m*g of the kinetic friction, so ... Your net force then is Fstatic - Fkinetic.
 
  • #3
thanks again I owe you!
 

1. What is the difference between kinetic and static friction?

Kinetic friction is the force that opposes the motion of an object while it is in motion, whereas static friction is the force that opposes the motion of an object while it is at rest.

2. How do you calculate the net force when moving a block with kinetic and static friction?

The net force can be calculated by subtracting the force of kinetic friction from the force of static friction. This will give you the overall force acting on the block.

3. How does the coefficient of friction affect the net force?

The coefficient of friction is a measure of how easily two surfaces slide against each other. It directly affects the force of friction, therefore it also affects the net force acting on the block.

4. Can the net force ever be greater than the force of static or kinetic friction?

No, the net force can never be greater than the force of static or kinetic friction. The maximum amount of force that can be applied to an object without causing it to move is equal to the force of static friction.

5. How can you decrease the force of friction when moving a block?

The force of friction can be decreased by using a lubricant or by reducing the weight of the object. Additionally, increasing the surface area of the object in contact with the surface it is sliding on can also decrease the force of friction.

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