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A man floating on a raft in water flowingat 2kmph observesa motor lauch overtakinghim at t = 0. Then lauch travels withthe speed of 20kmp relativeto still water . After travellingfor a time of 1 hr , thelauch turns back towards raft.How far from from the original point of crossing do they meet and whatis the total time elapsed ? |
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Answer» Solution :Figureshows point A,B,C and Dalongbank . `A to` pointof crossing for firsttime . `B,D to` POSITIONS of raft and boat when boat turns back .  `C to ` Possitions of raft and boat during the second crossing . NOTE: If we fix the OBSEVER on the bank , raft has a speed of 2kph, boathas a speed of 20+2=22 kph fordistance AD and 20-2=18kph for distanceDC. Fix the observer on raft. W.r.t. raft, boathassamevelocityupstream as well ad downstream . Hence, if the boattravels for 1hr, while movingaway from raft, it travelsthe sametime while approachingthe raft,. `therefore ` timebetween two crossings =t=2h. We now FINDTHE distancetraveled by raft in2 hr `= 2 xx 2 = 4` km. |
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