1i guess wrng q....itz frm tmh aieee ..........
a boat moves wid speed 5km/h wrt water in starigh river flwoin wid a speed 3km/h n havin width 1km
: hw long will d boat take to make a round trip across d river
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19 Answers
1now i got the problem ..
it should have been mentioned !! I too was getting 1/2 at the start .
1so,ans. is as in #2 i wrote
2/5sin@ hrs.
@is angle boat makes with river flow
1@nishant sir and wats in name
wat u did in #13 i also did at first but then on reading it again u find this line
a boat moves wid speed 5km/h wrt water in starigh river flwoin wid a speed 3km/h n havin width 1km : hw long will d boat take to make a round trip across d river
the line i highlighted wat does it mean........it means river flows along its length not along width.
in that case question is written improperly by wats in name or it is
a wrong ques. itself.
62well mani i dont use formulas nor can i remember them.. ;)
but then yeah it is nto a bad idea..
and yeah in this question we all had understood the question wrongly
the river is a magical one and is flowing from one shore to the other :D
11sir can't we use the formula t=d/vsin@
where @ is the angle made by the swimmer with the horizontal
to be true
i could not get u!!!!!!
62oh got you
in that case the river somehow is flowing in the direction of the swimmer and the total time is given by
1/(5+3) + 1/(5-3) = 1/8+1/2 = 5/8 hours :P
62a boat moves wid speed 5km/h wrt water in starigh river flwoin wid a speed 3km/h n havin width 1km
: hw long will d boat take to make a round trip across d river
See the boat moves with 5 km/h at an angle of theta
so its velocity with respect to ground is
5 cos θ i + 5 sin θ j - 3 j
= 5 cos θ i + (5 sin θ - 3) j
this flows perpendicular which I am assuming because the question otherwise seems unclear...
So the net direction of flow becomes such that 5sin θ=3 so cos θ = 4/5
so the velocity in forward direction is 4km/h
so the time taken to go to the other side and come back will be given by 2km/4 = 1/2 hours!