QuestionJuly 2, 2025

Not including thinking distance, lawful brakes must stop a car at 20 miles per hour within how many feet? 25 feet 10 feet 30 feet 20 feet

Not including thinking distance, lawful brakes must stop a car at 20 miles per hour within how many feet? 25 feet 10 feet 30 feet 20 feet
Not including thinking distance, lawful brakes must stop a car at 20 miles per hour within how many feet? 25 feet 10 feet 30 feet 20 feet

Solution
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Answer

20 feet Explanation 1. Convert speed to feet per second 20 miles per hour is equivalent to \frac{20 \times 5280}{3600} = 29.33 feet per second. 2. Use stopping distance formula The stopping distance d in feet can be calculated using the formula d = \frac{v^2}{2g\mu}, where v is the velocity in feet per second, g is the acceleration due to gravity (32.2 ft/s²), and \mu is the coefficient of friction (typically around 0.7 for dry pavement). 3. Calculate stopping distance Substituting the values, d = \frac{(29.33)^2}{2 \times 32.2 \times 0.7} \approx 20 feet.

Explanation

1. Convert speed to feet per second<br /> 20 miles per hour is equivalent to $\frac{20 \times 5280}{3600} = 29.33$ feet per second.<br />2. Use stopping distance formula<br /> The stopping distance $d$ in feet can be calculated using the formula $d = \frac{v^2}{2g\mu}$, where $v$ is the velocity in feet per second, $g$ is the acceleration due to gravity (32.2 ft/s²), and $\mu$ is the coefficient of friction (typically around 0.7 for dry pavement).<br />3. Calculate stopping distance<br /> Substituting the values, $d = \frac{(29.33)^2}{2 \times 32.2 \times 0.7} \approx 20$ feet.
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