CBSE Class 11-science Answered
mam i dont know how to do this.plz answer.
Asked by | 31 Dec, 2011, 11:48: AM
Expert Answer
Here main thing is to note that the 1 one is trying to swim at an angle theta and reached directly at B. The 2 one try to swim straight and reach at C then he walk toB.
let the width of river =d=AB
and let BC=x.
let the time taken by first person to reach at B =t.
let the time traken by 2 person to reach at C= t1
and to reach from Cto B=t2
so t=t1+t2--------(1)
For the first person-----
from the figure--------
U COS(?)=d/t----(2)
U sin(?)=2
Sin(?)=2/U=2/2.5
means cos (?)=(?2.25)/2----(3)
from (2) and (3)
t=d/?2.25----(4)
For the 2one--------
t1=d/2.5-----(5)
( because for the 2 one the the drift perpendicular to the river is only due to his own velocity 2.5, as the river velocity is perpendicular to his velocity)
t1=x/2---(6)
( because the displacement of the 2 one along the river is only due to the river velovity as , his velocity is perpendicular to the river velocity)
from (5) and(6)
x=2d/2.5----(7)
now he cover some distance by walking
t2=x/v=2d/2.5v----(8)
from 1, 4, 5 and 8
d/?2.25=d/2.5+2d/2.5v
solve above expresiuon and find v.
Answered by | 13 Jan, 2012, 05:05: PM
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