Algebra 1 Common Core Student Edition, Grade 8-9

Common Core Performance Task

Using Skid M arks to Find the Speed of a Car

A driver on Pine Street applies his car’s brakes to avoid an accident. His car leaves
skid marks from Sanchez Street to Market Street, as shown in the diagram below.
Pine Street is paved with asphalt and the speed limit along Pine Street is 50 mi/h.

You can use the formula s = Y/30 fd to determine the approximate speed of a
car when it begins to skid, where s is the speed of the car in miles per hour,/is the
coefficient of friction, and d is the length of the skid marks in feet. Ihe coefficient
of friction is a value that depends on the surface material of the road, as shown in
the table below.

Pine St. _______________

\ ------

,. Skid m arks

Typical Coefficients

of Friction

Gravel 0.6

Asphalt 0.7

Cement 0.9

Task D escr i p t i o n

Determine whether the driver on Pine Street was traveling within the speed limit.
Then determine the maximum length of the skid marks left on Pine Street by a car
that travels within the speed limit. Round your answer to the nearest foot.

Connecting the Task to the Math Practices practices

As you complete the task, you'll apply several Standards for Mathematical
Practice.

• You'll use a triangle relationship to determine the length of the skid marks.
  (MP 1, MP 4)


• You’ll write and simplify a radical expression to find the speed of the car. (MP 6)


• You’ll graph a square root function to analyze the relationship between
  skid-mark length and speed. (MP 5)

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PowerAlgebra.com ^ Chapter 10 Radical Expressions and Equations 613