# How to find the coefficient of kinetic friction

• Ushitha Dissanayake
In summary, the speed of a 4.0-N hockey puck, sliding across a level ice surface, decreases at the rate of 0.61 m/s2. The coefficient of kinetic friction between the puck and ice is 0.1525.
Ushitha Dissanayake

## Homework Statement

The speed of a 4.0-N hockey puck, sliding across a level ice surface, decreases at the rate of 0.61 m/s2. The coefficient of kinetic friction between the puck and ice is:
A) 0.062
B) 0.25
C) 0.41
D) 0.62
E) 1.2

## Homework Equations

I'm not too sure but i know that :
If the body begins to slide along the surface, the magnitude of the
frictional force rapidly decreases to a value fk given by
fk =ukFN
where uk is the coefficient of kinetic friction

## The Attempt at a Solution

fk =ukFN
0.61=uk4
uk=0.61/4
uk=0.1525
But i was wrong

Hi Ushitha Dissanayake

Welcome to Physics Forums!

Don't be too quick to plug in numbers, It's easier to follow your work if you work symbolically as much as possible.

You can use the ##x_2## and ##x^2## icons in the edit panel header to create subscripts or superscripts for your text-mode equations. The ##\Sigma## icon gives you access to a menu of math symbols that you can also use.

Ushitha Dissanayake said:
fk =ukFN
0.61=uk4
uk=0.61/4
uk=0.1525
I don't understand the second line in the above. You seem to be equating an acceleration to a force? (It's hard to tell because there are no units associated with the numeric values). Is FN the normal force (weight of the puck)?

You know the weight (in Newtons) of the puck so you can find its mass, right? Since you're given the puck's acceleration, can you then use Newton's 2nd law to find the force acting on it?

Ushitha Dissanayake
Oh i see, i was actually just using the kinetic energy formula but i didn't properly realize that ƒk was the force of kinetic energy. Thanks for the help

Kinetic energy doesn't have a force. This is a question about force due to friction and one of Newton's laws.

In addition to all of the above comments, consider using the information that you have a 4.0 N puck as opposed to a puck with a different weight. You do not appear to have used that information in your attempted solution.

## 1. What is the coefficient of kinetic friction?

The coefficient of kinetic friction is a value that represents the amount of friction between two surfaces in motion. It is a dimensionless number that is determined by the properties of the materials in contact.

## 2. How is the coefficient of kinetic friction calculated?

The coefficient of kinetic friction can be calculated by dividing the force of kinetic friction by the normal force between two surfaces. This can be done through experiments or by using mathematical formulas.

## 3. What factors affect the coefficient of kinetic friction?

The coefficient of kinetic friction can be affected by the nature and roughness of the surfaces in contact, the weight of the objects, and the presence of any lubricants or contaminants.

## 4. Why is the coefficient of kinetic friction important?

The coefficient of kinetic friction is important because it helps us understand and predict the amount of friction between two surfaces in motion. This can be useful in designing machines and structures, as well as in everyday situations such as driving or walking.

## 5. How can the coefficient of kinetic friction be reduced?

The coefficient of kinetic friction can be reduced by using lubricants, polishing or smoothing the surfaces, or changing the materials in contact to ones with lower coefficients of friction. Additionally, increasing the surface area of contact can also decrease the coefficient of kinetic friction.

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