MikeCottTrials Posted April 2, 2011 Report Share Posted April 2, 2011 Hey guys, as always I think this forum could be a life line for me... A car is initially at 18km per hour and travels at this velocity for 44 seconds; it then accelerates to 45 km per hour in 30 seconds and stays at this velocity for 56 seconds. What is the total distance covered by the car in the 130 seconds described? This is how I've calculated it... 18000/60/60=5, 5*44=220 45-18=27, 30/27=0.9, 1/2 (5+12.5)*30=262.5 45000/60/60=12.5, 12.5*56=700 220+262.5+700=1182.5 Answer: 1.18km Just looking for some reassuring, you are correct sir... or you are wrong and here is why Quote Link to comment Share on other sites More sharing options...
Oli P Posted April 2, 2011 Report Share Posted April 2, 2011 You are correct, but why have you got 30/27=0.9 in there? Quote Link to comment Share on other sites More sharing options...
DrDoom Posted April 2, 2011 Report Share Posted April 2, 2011 http://jforjustice.co.uk/banksters Quote Link to comment Share on other sites More sharing options...
MikeCottTrials Posted April 2, 2011 Author Report Share Posted April 2, 2011 You are correct, but why have you got 30/27=0.9 in there? Maybe I was testing peoples attention maybe I wasn't sure what I was doing is also a possible explanation Quote Link to comment Share on other sites More sharing options...
Simpson Posted April 2, 2011 Report Share Posted April 2, 2011 Yar your right Quote Link to comment Share on other sites More sharing options...
Tomm Posted April 3, 2011 Report Share Posted April 3, 2011 The first and last bits are easy. Second bit you need to use s= ½(u+v)t which I think you've got. The extra working out you did (45-18=27, 30/27=0.9*) works out the acceleration (although you've done it kph/s which is likely to confuse matters) and isn't really necessary - it just adds another step. You could however calculate the acceleration in m/s/s and then substitute that into s= ut+ ½at² to give you the distance over the middle part of the journey (262.5m). *30/27 doesn't equal 0.9 Quote Link to comment Share on other sites More sharing options...
MikeCottTrials Posted April 4, 2011 Author Report Share Posted April 4, 2011 Thanks for the help guys! As always really appreciate your input Quote Link to comment Share on other sites More sharing options...
PaRtZ Posted April 4, 2011 Report Share Posted April 4, 2011 Yar your right best way of doing it for me. Got to love geometry.... Quote Link to comment Share on other sites More sharing options...
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