Question

the stopping distance of an automobile is directly proportional to the square of its speed v. a car required 90 feet to stop when its speed was 70 miles per hour. find a mathematical model that gives the stopping distance d in terms of its speed v. Estimate the stopping distance if the brakes are applied when the car is traveling at 71 miles per hour.

Answer 1

First we write the mathematical model in a generic way:
"The stopping distance of an automobile is directly proportional to the square of its speed v"
d = kv ^ 2
Where,
k: proportionality constant.
We now look for the value of K:
d = kv ^ 2
90 = k ((70) * (5280/3600)) ^ 2
k = 90 / ((70) * (5280/3600)) ^ 2
k = 0.008538539 s ^ 2 / feet
The equation will then be:
d = (0.008538539) * v ^ 2
For v = 71 miles per hour we have:
d = (0.008538539) * ((71) * (5280/3600)) ^ 2
d = 92.6 feet
Answer:
a mathematical model that gives the stopping distance in terms of its speed v is:
d = (0.008538539) * v ^ 2
The stopping distance if the brakes are applied when the car is traveling at 71 miles per hour is:
d = 92.6 feet