ShmoopTube

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It's time for your daily dose of Shmoop... ...so open wide.

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Shuffleboard, if you haven't heard of it, is an "old people" sport that retirees play

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on cruise ships.

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Grandma or Grandpa stands at one end of a narrow lane, and a grid of spaces with various

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scores is at the other end.

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With a push of the broom, a puck... which is called a biscuit,

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and no, we're not making that up... goes flying down the lane, hopefully coming to a stop

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at the perfect spot.

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It's like curling for people without convenient access to ice.

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If an elderly player is able to give the 4 kilogram biscuit an initial speed of 5 meters

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per second, and it comes to rest after 10 meters, what

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is the coefficient of friction between the biscuit and the court?

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And here are the possible answers...

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This problem is a two-parter.

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We first have to find how fast the biscuit is decelerating,

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then find the coefficient of friction.

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Keep in mind that there is no correlation between this and how fast

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your biscuit decelerates after you send it sliding down your esophagus.

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First, we know that the biscuit is moving at 5 meters per second initially,

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and decelerates to a stop in 10 meters.

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Not a lot of information, but it's enough.

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We can use v squared = v initial squared plus 2 a x, as our core formula.

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Plugging in what we know, we get 0 squared is equal to... 5 squared plus 2a times 10.

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With some simple algebra, we get -25 is equal to 20a,

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so a is equal to -5/4 meters per second squared.

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Now that we have our acceleration, this problem is easy.

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F = ma, and then F = u times the normal force.

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First, to find out how much force friction is applying to the biscuit, we multiply the

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mass of the biscuit by the acceleration, which we found in the last part.

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4 kilograms times -5/4 meters per second is equal to 5 Newtons of force.

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Sure... go ahead and chase that biscuit with a few Fig Newtons...

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Finally, the force of friction is equal to mu times the normal force.

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The force of friction is equal to -5 Newtons, so we plug that into the equation.

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We're missing the normal force, but since the biscuit is on a flat plane,

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that's just equal to mass times acceleration due to gravity, or 4(-10).

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Solving for mu, we get that the coefficient of friction is equal to 1/8...

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...or choice (A).

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Now to deal with the friction in Grandma and Grandpa's relationship...

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