A swimmer can cross a river flowing at uniform
speed of width 400m in a shortest possible time
interval of 80 secs. If the same swimmer needs
to swim across in a direction such that he
reaches the point directly opposite his starting
position (A to B in diagram) then his time of
crossing increases to 100 sec. Assuming his
swimming speed with respect to still water to be
uniform and same in both cases, the flow
velocity of the river is ?
Answers
Explanation:
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11th
Physics
Motion in a Plane
Relative Motion in 2 Dimension
A swimmer crosses a river w...
PHYSICS
A swimmer crosses a river with minimum possible time 10 second. And when he reaches the other end starts swimming in the direction towards the point from where he started swimming. Keeping the direction fixed the swimmer crosses the river in 15 sec. The ratio of speed of swimmer with respect to water and the speed of river flow is:
(Assume constant speed of river & swimmer)
ANSWER
A swimmer crosses
v = velocity of man w.r.t . river
u =velocity of river
A
→
t
B=
v
d
⇒10=
v
d
⇒d=10V→(1)
B
→
t
C=
vcosθ
d
⇒15=
vcosθ
d
⇒d=15vcosθ→(2)
(1) & (2)⇒cosθ=
3
2
⇒secθ=
2
3
.
∵tanθ=
v
u
∴
sec
2
θ−1
=
v
u
⇒
v
u
=
4
9
−1
=
2
5
⇒
u
v
=
5
2
Answer:
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Explanation:
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