BOATS & STREAMS
In water, the
direction along the stream is called downstream. And, the direction against the
stream is called upstream.
If the speed of a
boat in still water is u kmph and the speed of the stream is v kmp, then
Speed down steam is (u + v) kmph
Speed up steam is (u - v) kmph
If the speed
downstream is a (u + v) kmph and the speed upstream is b (u - v) kmph, then
Speed in still water is (a + b)/2 or
((u + v) + (u - v))/2
Rate of stream is (a - b)/ 2 or ((u +
v) – (u – v))/2
1
Speed of a swimmer is 8
kmph in still water. If the rate of stream is 3 kmph, find the effective speed
of the swimmer downstream?
a) 10 kmph b) 11 kmph c) 12 kmph d)
15 kmph
u + v
8 + 3
11 kmph
2
Speed of a man is 8 kmph
in still water. If the rate of current is 3 kmph, find the effective speed of
the man upstream?
a) 10 kmph b) 5 kmph c) 12 kmph d)
15 kmph
u - v
8 - 3
5 kmph
3
A man can row upstream
at 10 kmhr and downstream at 16 kmph. Find the man’s rate in still water?
a) 10 kmph b) 13 kmph c) 12 kmph d)
15 kmph
u + v = 16 kmph
u - v = 10 kmph
(u + v) + (u - v) = 16 + 10
2u = 26
u = 13 kmph
4
A man can row upstream
at 10 kmhr and downstream at 16 kmph. Find the rate of current?
a) 10 kmph b) 3 kmph c) 12 kmph d)
15 kmph
u + v = 16 kmph
u - v = 10 kmph
(u + v) - (u - v) = 16 - 10
2v = 6
v = 3 kmph
5
A man takes twice as
long to row up as to row down the river. If the rate of river is 4 kmph, find
the rate of the man in still water?
a) 10 kmph b) 12 kmph c) 14 kmph d)
15 kmph
(u + v) = 2 (u - v)
v = 4
(u + 4) = 2 (u - 4)
(u + 4) = (2u - 8)
U = 12 kmph
6
The speed of a boat in
still water is 8 kmph and the rate of current is 4 kmph. The distance travelled
downstream and upstream in 5 minutes is?
a) 1/3 km, 1 km b) 1 km, 1/3 km c) 2 km, 3 km d) 3 km, 2km
u + v
8 + 4
12 kmph
5 minutes = (5/60) hours
D = 12 kmph x 5/60
D = 1 km
u - v
8 - 4
4 kmph
5 minutes = (5/60) hours
D = 4 kmph x 5/60
D = 1/3 km
7
The speed of a boat in
still water is 6 kmph and the speed of the stream is 1.5 kmph. A man rows to a place
at a distance of 22.5 km and comes back to the starting point. Find the total
time taken by him?
a) 3 hours b)
5 hours c) 8 hours d) 12 hours
6 + 1.5
7.5 kmph
22.5 km = 7.5 kmph x T
T = 3 hours
6 – 1.5
4.5 kmph
22.5 km = 4.5 kmph x T
T = 5
3 + 5
8 hours
8
A man can row 6 kmph in
still water. When the river is running at 1.2 kmph, it takes him 1 hour to row
to a place and back. How far is the place?
a) 3 km b) 2.88 km c) 2 km d)
5 km
6 + 1.2
7.2 kmph
6 – 1.2
4.8 kmph
7.2 x 4.8/ (7.2 + 4.8)
2.88 kmph
D = 2.88 kmph x 1 hour
D = 2.88 km
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