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# HP 20S and HP 21S: Approximating Stopping Distances

HP 20S and HP 21S:  Approximating Stopping Distances

Introduction

We can approximate the stopping distance (in feet) of a vehicle on dry pavement given the vehicle’s speed (in miles per hour, mph) by the formula:

y = 3.85714285714*10^-2 * x^2 + 1.44504201681 * x + 0.64915966369

or

y = 27/200 * x^2 + 1.44504201681 * x + 0.64915966369

y:  stopping distance on dry pavement, feet
x:  speed of vehicle, mph

Assumptions:

*  The vehicle is assumed to be a passenger vehicle.

*  The reaction time is 1 second and the deceleration rate is 28 ft/s.

The program listed rounds all results to one decimal place.

HP 20S and HP 21S Program: Stopping Distance

The key codes for both calculators are the same in this program.

STEP KEY    KEY CODE
01   LBL B  61, 41, b
02   STO 0  21, 0
03   x^2    51, 11
04   ×      55
05   2      2
06   7      7
07   ÷      45
08   7      7
09   0      0
10   0      0
11   +      75
12   RCL 0  22, 0
13   ×      55
14   1      1
15   .      73
16   4      4
17   4      4
18   5      5
19   0      0
20   4      4
21   2      2
22   0      0
23   1      1
24   6      6
25   8      8
26   1      1
27   +      75
28   .      73
29   6      6
30   4      4
31   9      9
32   1      1
33   5      5
34   9      9
35   6      6
36   6      6
37   3      3
38   9      9
39   =      74
40   STO 1  21, 1
41   FIX 1  51, 33, 1
42   RTN    61, 26

Examples

Input:  25 mph,  Result:  60.9 ft

Input:  40 mph,  Result:  120.2 ft

Input:  65 mph,  Result:  257.5 ft

Note:  This time I am writing this blog entry direct in the Blogger compose box.  When I transfer text from either Jarte or WordPad to Blogger, all the formatting is lost.  And I don’t want to format my text twice.  I will still save a backup copy.  I am very happy that Blogger compose box allows me to select special characters for the math symbols I need (the happy face is appropriate because it makes me happy!)

Source:

Glover, Thomas J.  Pocket Ref 4th Edition.  Sequoia Publishing, Inc. Littleton, CO. 2012
Eddie
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