X-Google-Language: ENGLISH,ASCII X-Google-Thread: f442a,aa366a233ab00d91 X-Google-Attributes: gidf442a,public X-Google-Thread: f996b,53f9f7cceb4d817f X-Google-Attributes: gidf996b,public X-Google-Thread: 107d75,4a81179a975b6945 X-Google-Attributes: gid107d75,public X-Google-Thread: 10b271,aa366a233ab00d91 X-Google-Attributes: gid10b271,public X-Google-ArrivalTime: 2002-03-28 14:01:49 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!newsfeed1.cidera.com!Cidera!cyclone.socal.rr.com!cyclone3.kc.rr.com!news3.kc.rr.com!twister.socal.rr.com.POSTED!not-for-mail Message-ID: <3CA392FA.1020903@alum.rpi.edunospamm> From: Chris Wiegand User-Agent: Mozilla/5.0 (Windows; U; Win 9x 4.90; en-US; rv:0.9.4) Gecko/20011128 Netscape6/6.2.1 X-Accept-Language: en-us MIME-Version: 1.0 Newsgroups: alt.ascii-art,alt.flame.jesus.christ,sci.physics,alt.sci.physics Subject: Re: A question for those interested in physics... References: <56c45acf.0203281214.7c24b70a@posting.google.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Lines: 45 Date: Thu, 28 Mar 2002 22:01:31 GMT NNTP-Posting-Host: 66.91.81.204 X-Complaints-To: abuse@rr.com X-Trace: twister.socal.rr.com 1017352891 66.91.81.204 (Thu, 28 Mar 2002 14:01:31 PST) NNTP-Posting-Date: Thu, 28 Mar 2002 14:01:31 PST Organization: RoadRunner - West Xref: archiver1.google.com alt.ascii-art:16361 alt.flame.jesus.christ:74462 sci.physics:165011 alt.sci.physics:18380 Jonas M�ller wrote: > Edwin wrote in message news:... > >>"Robert Bowmaker" wrote in >>news:x7Vn8.1094$sO2.220418@news.xtra.co.nz: >> >> > >>>The question is: What actually happens to the bullet? Does it go into >>>space? Does it fall back down? Does it burn up? None of the above? >>> > > I got a bit interested in this problem so I tried to solve it, at > first mathematically but thats a bit difficult. > I came up to this differential equation > > V(t) = V(0) -g*t -cw*A*rho*t/2/M*(V(t))^2 > I set up an equation for free fall, where it is assumed by Stokes equation that the drag force is directly proportional to velocity. So I got the following: Fnet = mg - Dv where D is a drag coefficient ma = mg - Dv a = g - Dv/m d^2x/dt^2 = g - (D/m)*dx/dt using d^2x/dt^2 = gexp(-bt); because a(0) = g one gets that, dx/dt = mg/D(1-exp(-bt)); because a(infinity) = 0, so v(infinity) = mg/D= terminal velocity = (vT) using dv/dt = a one finds that b = D/mg = 1/(vT) so from integration of v(t) x(t) = (vT)t + (vT)*exp(-t/vT) + x(0)