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# The distance d (in feet) that it takes a car to come to a complete stop

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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.

Apr 11, 2018

### Best Answer

#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.

Apr 11, 2018

### 1+0 Answers

#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