The distance *d* (in feet) that it takes a car to come to a complete stop on dry asphalt can be modeled by *d* = 0.05s^2 + 1.1s where *s* is the speed of the car (in miles per hour). A car has 78 feet to come to a complete stop. Find the maximum speed at which the car can travel.

GAMEMASTERX40
Apr 11, 2018

#1**+2 **

We can already plug in 78 for d in this equation.

78 = 0.05s^2 + 1.1s

After subtracting 78 from both sides, we have:

0.05s^2 + 1.1s - 78 = 0.

Solving this quadratic, we have: s = 30.0000000000000004, -52.00000000000001

The last time I checked, we can’t go negative speed, so s = 30

It is actually 30.000000000000004, but just round it down.

supermanaccz
Apr 11, 2018

#1**+2 **

Best Answer

We can already plug in 78 for d in this equation.

78 = 0.05s^2 + 1.1s

After subtracting 78 from both sides, we have:

0.05s^2 + 1.1s - 78 = 0.

Solving this quadratic, we have: s = 30.0000000000000004, -52.00000000000001

The last time I checked, we can’t go negative speed, so s = 30

It is actually 30.000000000000004, but just round it down.

supermanaccz
Apr 11, 2018