LeOCruX Posted February 18, 2008 Report Share Posted February 18, 2008 Primul semestru de fizica m'a facut sa cred ca aceasta materie e usoara, dar a doua ora de fizica din al doilea semestru .... a dovedit contrariul.Am pentru maine o tema la fizica care nu stiu sa o fac si cer ajutorul vostru ( sunt in cls a VI-a )Un mobil se deplaseaza pe jumatate din distanta de parcurs cu viteza v1 = 54 km/h, iar pe cealalta jumatate din distanta, cu viteza v2 = 25 m/s. Care este viteza medie pe intregul parcurs?P.S. In carte zice ca e 18.75 m/s ... de unde i-a dat asta nu stiuP.S.#2 Daca incalc vre'o regula inchideti topicul (stergetil')P.S.#3 Nu m'a luati drept un prost Quote Link to comment Share on other sites More sharing options...
H4e Posted February 18, 2008 Report Share Posted February 18, 2008 Deci esti sigur k la prima e km/h shi la a doua e m/s????Daca e acelashi unitate de masura km/h la ambele sau m/s la ambele atunci teoretic ar terbui sa fie m,edia aritmetica a celor doua viteze dar aia e 28 mai zice ceva la probl??? Quote Link to comment Share on other sites More sharing options...
H4e Posted February 18, 2008 Report Share Posted February 18, 2008 Deci dak e asha dupa kteva calcle mia iesit media aritmetica la 25 m/s shi 13,(3) m/s adik 54 km/h shi media lor da 19,1!mai zi odata probl k in carte!P.S: srry pt double post Quote Link to comment Share on other sites More sharing options...
LeOCruX Posted February 18, 2008 Author Report Share Posted February 18, 2008 nu , nu mai zice nimica problema ... 28 m/s sau km/h ? Quote Link to comment Share on other sites More sharing options...
Nytro Posted February 18, 2008 Report Share Posted February 18, 2008 v1 = 54 km/h = 54000m/3600sec = 15m/secv2 = 25 m/sv=(v1+v2)/2 = (25+15)/2 = 40/2 = 20m/secCel putin asa cred ( am media 5 la fizica ) Quote Link to comment Share on other sites More sharing options...
LeOCruX Posted February 18, 2008 Author Report Share Posted February 18, 2008 H4e ... problema nu zice dar d1=d2 (distanta ....)Nytro ... ceva in genul asta am facut si eu dar raspunsule in carte e 18.75 (((( si sigur asta e . Quote Link to comment Share on other sites More sharing options...
H4e Posted February 18, 2008 Report Share Posted February 18, 2008 Srry am greshit nytro are dreptate insa dak zici k la rasp e altceva oi fi copiat u greshit probl , ori teai uitat la rasp greshit, ori raspunsul e greshit. Quote Link to comment Share on other sites More sharing options...
Nytro Posted February 18, 2008 Report Share Posted February 18, 2008 Pai nu prea vad de ce ar fi 18 ... Din moment ce merge cu o anumita viteza 1/2 din traseu si cealalta jumatate cu alta viteza , viteza medie e media aritmetica a vitezelor . Poate nu ai citit bine problema . Quote Link to comment Share on other sites More sharing options...
vladiii Posted February 18, 2008 Report Share Posted February 18, 2008 Vm=viteza medied=distantat=timpult1=timpul parcurs in prima jumatate a drumuluit2=timpul parcurs in a 2-a jumatate a drumuluiv1, v2=viteza in cele 2 jumatati de drumCum vitezele sunt constate (acceleratia este 0), atunci:Vm=d/tt=t1 + t2Evident: d/2=v1 * t1; d/2=v2 * t2;=> t1=d/(2*v1);=> t2=d/(2*v2);Adunam relatiile de mai sus:=> t1+t2=(d/2) * [(1/v1) + (1/v2)]=(d/2) * [(v1+v2)/v1*v2];Cum am spus mai sus:Vm=d/tInlocuiesc pe t cu t1+t2.=> Vm=d * (2/d) * [v1*v2/(v1+v2)];Dupa simplificari => Vm=2*v1*v2/(v1+v2).Cum v1=25 m/s, iar v2=54 km/h=15 m/s:=> Vm=2*25*15/40 = 750/40 = 18.75 m/s Bafta maine la ora de fizica Quote Link to comment Share on other sites More sharing options...
Nytro Posted February 18, 2008 Report Share Posted February 18, 2008 Asta vroiam si eu sa zic Quote Link to comment Share on other sites More sharing options...
LeOCruX Posted February 18, 2008 Author Report Share Posted February 18, 2008 Mersi Mult... Sa traiesti Quote Link to comment Share on other sites More sharing options...
SlothMaster Posted February 18, 2008 Report Share Posted February 18, 2008 din câte ºtiu io ... cand se calculeaza viteza medie a unui mobil se foloseste media armonica :wink: asa iti iese 18.75 km/h Quote Link to comment Share on other sites More sharing options...