# Average Coefficient of Kinetic Friction between Ice and Puck

• K Wils
In summary, a hockey puck with an initial speed of 11.6 m/s on a frozen lake slows down to 7.4 m/s after 5 seconds. Its average acceleration is calculated to be -0.84 m/s squared. However, the average value of the coefficient of kinetic friction between the puck and the ice cannot be negative, as it represents the resistance to motion. Upon checking the calculations, it was found that the negative sign was due to forgetting to consider directions. The correct answer for the coefficient of kinetic friction is 0.0857.
K Wils
1. The problem: A hockey puck is hit on a frozen lake and starts moving with a speed of 11.6 m/s. Five seconds later, its speed is 7.4 m/s. What is its average acceleration? The acceleration of gravity is 9.8 m/s. Answer in units of m/s. What is the average value of the coefficient of kinetic friction between puck and ice?

## Homework Equations

: [/B]Sum of the forces' x-components equals mass times acceleration. Sum of the forces' y-components equals zero. Kinetic friction equals the coefficient of kinetic friction times the normal force.

## The Attempt at a Solution

: [/B]I solved for the acceleration earlier and got -0.84 m/s squared. I did this by taking the difference in velocities and dividing by the time (7.4 - 11.6 = - 4.2. - 4.2 / 5 = - 0.84). I then applied what I knew about the normal force: FN=mg. I also knew that FK=μkFN. Therefore, FK=μk(mg). While ∑Fx=ma, μk(mg)=ma. The masses cancel out. Then I put in my numbers: μk(9.8 m/s squared)= - 0.84 m/s squared. From there I divided my acceleration by 9.8 and got μk= - 0.0857. I checked it and the system on the website I was using for homework (UT) deemed my answer incorrect. Can anyone help?

You can't have a negative coefficient of friction.

P.S. Welcome to Physics Forums.

Your work is correct but you have forgotten to take into account directions. Part (i) has the correct answer, as for part (ii), as @TomHart mentioned, you can't have a negative coefficient of friction. What do you think your mistake is then, and why?

I had realized that shortly after posting the thread. Thank you for the help though! I really appreciate it!

## 1. What is the average coefficient of kinetic friction between ice and a puck?

The average coefficient of kinetic friction between ice and a puck is approximately 0.03. This means that for every unit of force applied to the puck, there is a 0.03 unit of force acting in the opposite direction due to friction.

## 2. How is the average coefficient of kinetic friction between ice and a puck determined?

The average coefficient of kinetic friction between ice and a puck is determined through experiments and calculations. A puck is placed on a flat sheet of ice and a known force is applied to it. The distance the puck travels before coming to a stop is measured, and the force and distance values are used to calculate the coefficient of kinetic friction.

## 3. Does the average coefficient of kinetic friction between ice and a puck vary?

Yes, the average coefficient of kinetic friction between ice and a puck can vary depending on factors such as temperature, surface roughness, and the material of the puck. However, on average, it falls within the range of 0.02 to 0.05.

## 4. How does the average coefficient of kinetic friction between ice and a puck affect the speed of the puck?

The average coefficient of kinetic friction between ice and a puck has a significant effect on the speed of the puck. As the coefficient increases, the friction force acting against the puck also increases, causing it to slow down faster. This can affect the overall speed and movement of the puck on the ice.

## 5. Can the average coefficient of kinetic friction between ice and a puck be reduced?

Yes, the average coefficient of kinetic friction between ice and a puck can be reduced by using materials that have a lower coefficient of friction, such as certain types of synthetic ice. Additionally, reducing the temperature of the ice can also decrease the coefficient of friction, allowing for smoother and faster puck movement.

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