Date: Sun, 27 Apr 2003 22:00:18 GMT From: "someguy" <someguynopsamwhere.se> Subject: Re: Speeding Tales/Help
"J. Harris" <insectoatmindspring.com> wrote in news:b8h71h$j86$1nopsam.atl.mindspring.net... > I was thinking of dropping a pen from a predetermined height, then asking > the officer to guess its speed as it hit the ground; problem is, I can't > recall the mathematic formula for that example... Time to "Ask Jeeves". > -- This is elementary physics: First calculate the time from releasing the pen to the pen hitting the ground. This is done by using the formula height=acceleration*time^2/2, i.e. time=sqr(2*height/acceleration) With an acceleration of 9.81 m/s^2 this gives a time of 0.45 s when the pen is dropped from an altitude of 1 m Now insert the time into the expression velocity=acceleration*time For a time of 0.45 s this gives a speed of 4.4 m/s or approximately 16 km/h if the pen is dropped from 1 m height. One can of course insert the expression for time directly into the velocity and obtain velocity=sqr(2*height*acceleration) All these formulas assume that you drop a pen that is not moving at the time of release! From this you can conclude that if a person falls from 1 m altitude (in horisontal position) he cannot absorb the fall using his arms only. The arms can handle a body moving at about 7 km/h (another very good reason for always using your safety belt!) -- someguy
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