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![[Post New]](/templates/default/images/icon_minipost_new.gif) 10 Jun 2007 14:31:36 IST
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A car travelling at 60km/hr overtakes another car travelling at 42 km/h.Assuming each car to be 5m long,find the time taken during the overtake and the total road distance used for the overtake. *This sum is from HC VERMA BOOK1 PAGE 52 Q.NO.22.AND THE ANS ARE2S AND 38 M RESPECTIVELY. pLEASE GIVE THE EXPLAINATION IN DETAIL STEP BY STEP.
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10 Jun 2007 14:53:54 IST
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Wait I m posting it in the evening.
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it is not important where u stand, but in which direction u are moving |
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hi savvej see let car with velocity 60km/hr be car A & the other be car B velocity of car A w.r.t car B = 18km/hr = 5m/sec therefore it's clear that car A will overtake car B in 2sec (see fig.) CLICK ON THE FIGURE TO ENLARGE
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10 Jun 2007 15:17:47 IST
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use the relative velocity concept
velocity of car 1 is 60x5/18=50/3 m/s
velocity of car 2 is 42x5/18=35/3 m/s
relative velocity of car1 with respect to car 2 is 50/3-35/3=15/3=5 m/s
car 1 has to travel a distance of 5+5 =10 m to overtake car2 (try to visualise)
hence time t to overtake car 2= 10/5 = 2 seconds
am solving for total distance
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10 Jun 2007 15:25:39 IST
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what about distance
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10 Jun 2007 15:26:51 IST
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also total road distance covered during overtake is equal to the total distance covered by car A(i.e car moving with 60kmph) now distance travelled by car A in 2 seconds is 33.33 sec but this distance is travelled by the centre of the car. so total distance coverd is 33.33 + 2.5 + 2.5 = 38.33 = 38m approx (see fig) CLICK ON THE FIGURE TO ENLARGE
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10 Jun 2007 15:27:55 IST
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i've now posted the soln. for distance. rate me if u understood if not then do ask ur doubt cheers
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10 Jun 2007 15:31:22 IST
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exactly you get 38.333 m approx 33
bye!
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10 Jun 2007 15:35:13 IST
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sorry 38
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10 Jun 2007 15:38:40 IST
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why the centr of the car and why not the head of the car to the head of the car?
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10 Jun 2007 15:43:51 IST
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apurv please tell me how did u calculate/?
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10 Jun 2007 15:45:45 IST
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ans. will be same in this case also u can take any head to head , centre to centre or tail to tail  in all the three cases ans. will be same see the fig. for head to head case below
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10 Jun 2007 16:10:17 IST
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priyesh has explained really well
ur right
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10 Jun 2007 22:47:31 IST
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an alternative approach
let t be the time in which the car overtakes the other.
now speed of first car is 11.67m/s and that of the 2nd car is 16.67m/s.now the 2ndcar has to cover an extra 10m also.
16.67t=11.67t + 10
=> t=2 sec
distance covered by 2nd car in 2 sec=33m(approx)
now total road distance will also cover the length of the car which is 5m
so, total road distance used for overtaking =38m
rate me if it helps but don't boink if it doesn't
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