# Thread: Estimating Speed of a Vehicle

1. ## Estimating Speed of a Vehicle

The speed a vehicle was traveling, s, in miles per hour, when the brakes were first applied, can be estimated using the formula:

where d is the length of the vehicle's skid marks, in feet.

a) Determine the speed of a car that made skid marks 4ft long.

b) Determine the speed of a car that made skid marks 16ft long.

c) Determine the speed of a car that made skid marks 256ft. long.

2. Originally Posted by camstill
The speed a vehicle was traveling, s, in miles per hour, when the brakes were first applied, can be estimated using the formula:

where d is the length of the vehicle's skid marks, in feet.

a) Determine the speed of a car that made skid marks 4ft long.

b) Determine the speed of a car that made skid marks 16ft long.

c) Determine the speed of a car that made skid marks 256ft. long.
Well then, these look like plug and chug kind of problems. They are all done the same way. Here's the first one.

$s=\sqrt{\frac{d}{0.04}}$

$s=\sqrt{\frac{4}{0.04}}$

$s=\sqrt{100}$

$s=10$ miles/hr

3. ## Thanks, but...........

I can't figure out the 2nd step to get to the 3rd step? Can you elaborate? Thank you!

4. Originally Posted by camstill
I can't figure out the 2nd step to get to the 3rd step? Can you elaborate? Thank you!
In the second step, after I substituted 4 for d, I divided 4 by .04.

$4 \div .04=4 \div \frac{4}{100}=\frac{4}{1} \times \frac{100}{4}=\frac{400}{4}=100$

5. ## Silly me......

I was forgeting the radical sign. Thank you so much for the help!