Question

choose the right answer.
what is the first speed at which the ratio of stopping distance to speed is greater than 3 to 1?

Explanation:

Step1: Calculate ratio for 20 mph

For speed \(v = 20\) mph and stopping - distance \(d=43\) feet. The ratio \(\frac{d}{v}=\frac{43}{20}=2.15\)

Step2: Calculate ratio for 30 mph

For speed \(v = 30\) mph and stopping - distance \(d = 79\) feet. The ratio \(\frac{d}{v}=\frac{79}{30}\approx2.63\)

Step3: Calculate ratio for 40 mph

For speed \(v = 40\) mph and stopping - distance \(d = 126\) feet. The ratio \(\frac{d}{v}=\frac{126}{40}=3.15\)

Answer:

\(40\) mph