a) 5 minutes
A man can swim in still water at 15 kmph. The river flows at 10 kmph. If he wants to cross the river
along shortest path, he should swim along a direction making an angle () with the direction of the
stream. Then
b) sin(90° + 2/3) c) 90°+sin' (2/3)
d) zero
a) sin (2/3)
Answers
Answered by
1
Explanation:
Velocity of man with respect to river water, v=5kmh
−1
. This is greater than the river flow velocity. Therefore, he can cross the river directly (along the shortest path or no drift condition from flow velocity). The angle of swim,
θ=
2
π
+sin
−1
(
v
u
)
=90
o
+sin
−1
(
v
u
)
=90
o
+sin
−1
(
5
3
)=90
o
+37
o
=127
o
w.r.t. the river flow or 37
o
w.r.t. the perpendicular in upstream direction
b. Resultant velocity or velocity of mass will be
v
m
=
v
2
−u
2
=
5
2
−3
2
=4kmh
−1
In the direction perpendicular to the river flow.
c. time taken to cross the river
t=
v
2
−u
2
d
=
4kmh
−1
1km
=
4
1
h=15min
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