Coefficient of Kinetic Friction

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To find the average acceleration of the hockey puck, the change in velocity over time gives an acceleration of -1.2 m/s². The coefficient of kinetic friction can be determined without knowing the mass, as it cancels out in the equations derived from Newton's second law. The force acting on the puck is the frictional force, which is equal to the product of the mass, gravitational acceleration, and the coefficient of kinetic friction. By setting up the equations correctly, one can solve for the coefficient of kinetic friction using the acceleration and gravitational force. This approach allows for a solution that is independent of the puck's mass.
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"A hockey puck is hit on a frozen lake and starts moving with a speed of 12 m/s. Exactly 5.0 s later, its speed is 6.0 m/s. What's the puck's average acceleration? What is the coefficient of kinetic friction between the puck and the ice?"

I've calculated the acceleration, but I'm stuck when it comes to finding the coefficient of kinetic friction since I don't know the mass of the object.
 
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You don't need the mass of the object, just like when calculating how fast something accelerates towards the Earth you don't need to know its mass. :)
 
How would you calculate that without the mass, though?
 
Well, think about it. The force on the puck is mgµ, and its acceleration is F/m. Right?
 
Solve the equations algebraically and you will see that at some point the mass cancels out of the equation providing a solution independent of the mass.
 
Write Newton's second law for the puck. What forces acts on the puck?
 

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