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| Math Central | Quandaries & Queries |
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Question from Leria, a student: The model S= radical 30df describes the relationship between the speed of a car , the conditions of the road, and the length of the skid marks when the car slams on the brakes. S is the speed of the car in miles per hour, In an accident, a car makes skid marks 85 feet long. The coefficient of friction is 0.6. A witness says that the driver was traveling faster than the speed limit of 35 miles per hour. Can the witness's statement be correct? Use algebra to explain your answer. A: When trying to solve this problem, I believe that you must use substitution, but I was lost after that. Please help me solve the problem. Thanks. |
Hi Leria,
The expression you have is
S = √(30 × d × f) miles per hour.
You also know that d = 85 feet and f = 0.6. Hence
S = √(30 × 85 × 0.6) miles per hour.
Perform the multiplications and then take the square root. Is the value larger than35 miles per hour? Is the witness's statement correct?
I hope this helps,
Penny
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