The stopping distance d of an automobile is directly proportional to the square of its speed s. On one road, a car requires 75 feet to stop from a speed of 30 miles per hour. How many feet does the car require to stop from a speed of 48 miles per hour on the same road?

The car requires 192 feet to stop from a speed of 48 miles per hour on the same road

Step-by-step explanation:

∵ The stopping distance d of an automobile is directly

   proportional to the square of its speed s

- That means d ∝ s²

∴  

∵ A car requires 75 feet to stop from a speed of 30 miles per hour

∴ d = 75 feet

∴ s = 30 miles/hour

- Change the mile to feet

∵ 1 mile = 5280 feet

∴ 30 miles/hour = 30 × 5280 = 158400 feet/hour

∵  The car require to stop from a speed of 48 miles per hour

    on the same road

- Change the mile to feet

∴ 48 miles/hour = 48 × 5280 = 253440 feet/hour

∵  

- Substitute the values of by 75 feet, by 158400 feet/hour

   and by 253440 feet/hour

∴

∴  

- By using cross multiplication

∴ 25 × = 75 × 64

- Divide both sides by 25

∴  = 192 feet

The car requires 192 feet to stop from a speed of 48 miles per hour on the same road

so, converting firstly the mixed fractions to improper fractions and then "adding".