SOLUTION: Corbin was driving his car at a speed of r miles per hour, when he had to stop suddenly. It took the car 254 feet to stop. The formula relating the distance d in feet required to s

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Question 598399: Corbin was driving his car at a speed of r miles per hour, when he had to stop suddenly. It took the car 254 feet to stop. The formula relating the distance d in feet required to stop to the speed r in miles per hour is d=0.05r(squared)+r. To the nearest mile per hour, how fast was Corbin traveling just before he braked?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Corbin was driving his car at a speed of r miles per hour, when he had to stop suddenly.
It took the car 254 feet to stop.
The formula relating the distance d in feet required to stop to the speed r in miles per hour is d=0.05r(squared)+r.
To the nearest mile per hour, how fast was Corbin traveling just before he braked?
:
d = .05r%5E2%2Br
d = 254, find r
.05r%5E2%2Br = 254
A quadratic equation:
.05r%5E2+%2B+r+-+254 = 0
Use the quadratic formula to find r
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
In this problem; x=r; a=.05; b=1; c= -254
r+=+%28-1+%2B-+sqrt%281%5E2-4%2A.05%2A-254+%29%29%2F%282%2A.05%29+
Do the math and you should get a positive solution of:
r ~ 62 mph