Q1.
A person can row
1/10
km upstream in 12 minutes
and return in 8 minutes . Find the speed of man in still water .
Solution.
distance = speed x time
1/10
= speed x
12/60
(upstream)
=
1/2
km/h
1/10
= speed x
8/60
speed =
6/8
=
3/4
km/h
speed in still water =
=
5/8
km/h
Solution
Q2.
A person can swim a quarter of a km upstream in
7/2
minutes and return in
5/2
minutes . find the speed of current .
Solution
speed of current =
downstream speed - upstream speed /2
upstream speed is =
120/28
=
60/14
=
30 /7
km/h
downstream
speed = 6 km/h
speed of current =
=
42 - 30/14
=
12/14
=
6/7
km/h
Solution
Q3.
A boy can row 9
1/3
km/hr in stable water .
He take thrice as much time to row up than as to row down the equal distance . The speed of current is
Solution.
Let the speed of current is x km/h .
(
28/3
+ x) = 3
(
28/3
- x) ------------(1)
(∴ distance = speed x time
boy takes thrice time to cover same distance upstream .)
solving equation we get x =
14/3
km/h
Solution
Q4.
A boy swims 6 km/h downstream he swims 25 km upstream in 5 hours . find the speed of current .
Solution.
downstream speed is 6 km/h , upstream speed is 5 km/h .
speed of current =
downstream speed - upstream speed /2
=
6 - 5/2
=
0.5 km/h
Solution
Q5.
A man take 3 hrs to swim upstream 3 km, while he take same time to swim 15 km downstream . find the speed of current .
Solution.
upstream speed is 1 km/h
downstream speed 5 km/h
speed of current is =
5 - 1/2
= 2 km/h
Solution
Q6.
In a river for a boat upstream speed is half of downstream speed and the speed of current is 3 km/h . find the speed of boat in still
water
Solution.
As we know that if speed is in ratio 1 : 2 then ratio of time taken to travel the same distance is 2 : 1 . let speed of boat in still water
is x km/h
(x + 3) = 2(x - 3)
x = 9 km/h
Solution
Q7.
A boat can move at the speed of 13 km/hr in still water and speed of current is 4 km/h . Find time to travel 72 km upstream .
Solution.
t =
d/5
=
72/9
= 8 hrs
Note : upstream speed = speed still water - speed of current
= 13 - 4
= 9 km/h
Solution
Q8.
A motorboat covers 36 km in a hour in still water towards upstream it covers 56 km in 1 hr 45 min . find the time to cover
the same distance in the direction of river .
Solution.
speed of boat in still water is 36 km/h
upstream speed =
56/105
x 60 = 32 km/h
so,speed of river (flow) is 4 km/h
downstream speed is = 40 km/h
time to cover 56 km (downstream) =
56/40
1
16/40
=
1
2/5
= 1 hr 24 min .
Solution
Q9.
The speed of boat in still water is 38 km/h . In downstream , it moves 13.3 km in 19 min. find the distance covered in 36 min upstream.
Solution.
Downstream speed is
13.3/19
x 60 = 42 km/h
speed of water s 4 km/h
upstream speed = 34 km/h
distance covered in 36 min = 36 x
34/60
= 20.4 km
Solution
Q10.
A person can row a certain distance downstream in 9 hours and return in 12 hours . Speed of current is 3 km/hr , find the speed of person
in still water and one side distance .
Solution.
Let speed of person in still water is m km/hr.
9(m + 3) = 12(m - 3)
9m + 27 = 12m - 36
-3m = - 63
m = 21 km/hr
distance = 24 x 9 = 216 km
Short cut
=
Cr(TD + TU)/( TU - TD)
=
3(12 + 9)/12 - 9
=
3 x 21/3
= 21 km/hr
distance = 24 x 9 = 216 km
Solution
