Calculating Coefficient of Kinetic Friction from Given Forces

In summary, a 23.0 kg block requires a horizontal force of 76.0 N to set it in motion on a horizontal surface. Once in motion, a force of 60.0 N is needed to maintain constant speed. From this information, the coefficient of kinetic friction can be calculated to be 0.070. However, this is incorrect and the correct calculation should use 60.0 N instead of 16.0 N to represent the force required to overcome friction. The accelerative force and friction force are equal at constant speed, and any extra force will cause the body to accelerate.
  • #1
Ry122
565
2
A 23.0 kg block is initially at rest on a horizontal surface. A horizontal force of 76.0 N is required to set the block in motion. After it is in motion, a horizontal force of 60.0 N is required to keep the block moving with constant speed. Find the coefficients kinetic friction from this information.

my attempt:
After the block is in motion 60N is required to prevent it from accelerating.
Therefore what is left over must be used to overcome friction which is 16N.
Friction force = weight x coefficient of kinetic friction
16N=23x9.8 x ck
ck=.070
But this is incorrect.
What am i doing wrong?
 
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  • #2
60N is the force required to prevent it from accelerating, this is the same force to overcome friction. 16N isn't anything in this problem, it's just the difference between the force required to overcome static friction and the force required to overcome kinetic friction.

Replace 16N with 60N in your calculations and try again.
 
  • #3
When friction force and the accelerative force are equal speed is constant. Anything extra will cause the body to accelerate so the accelerative force isn't overcoming friction.
60n is used to determine the static friction.
 
  • #4
as you say you need the same force as friction to stay at constant velocity.

The question tells you there there is 60 N of friction when moving.

76 N is used to determine static friction.
 

1. What is kinetic friction?

Kinetic friction is a type of force that occurs when two objects are in motion and in contact with each other. It is caused by the microscopic roughness of their surfaces and acts in the opposite direction of the motion.

2. How is kinetic friction calculated?

Kinetic friction is calculated using the formula: Fk = μkN, where Fk is the kinetic friction force, μk is the coefficient of kinetic friction, and N is the normal force between the two objects.

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

Kinetic friction occurs when two objects are in motion, while static friction occurs when two objects are at rest. The coefficient of kinetic friction is usually lower than the coefficient of static friction.

4. How does the coefficient of kinetic friction affect the amount of friction?

The coefficient of kinetic friction is a measure of the roughness of the surfaces in contact. A higher coefficient means a rougher surface, which results in a greater amount of friction. Similarly, a lower coefficient means a smoother surface and less friction.

5. What are some real-world examples of kinetic friction?

Some common examples of kinetic friction include the movement of a car's tires on the road, the sliding of a book across a table, and the movement of a pen on a piece of paper. In all of these cases, the surfaces are in motion and in contact, resulting in kinetic friction.

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