Word problem intermediate algebra

Question

A car with good tread can stop in less distance than a car with poor tread. A model for the stopping distance d, in feet, of a car with good tread on dry cement is
d = 0.04v2 + 0.5v, where v is the speed of the car in miles per hour. If the driver must be able to stop within 70 ft, what is the maximum safe speed of the car? Round to the nearest whole number.

Answer 1

Because the stop distance is 70 ft, from the formulae of the stopping distance d, we have:

 

d = 0.04v2 + 0.5 v

 

70 = 0.04v2 + 0.5v    or    0.04v2 + 0.5v -70 = 0

 

You have to resolve this quadratic equation to get the requested speed  ( I got 50 mph).

 

I hope it helps you.