1. The speed of a boat in still water is 15 km/hr and the speed of the current is 5 km/hr. the distance (in km) travelled by the boat downstream in 15 minutes is
(a) 4
(b) 5
(c) 6
(d) 8
2. The speed of a boat is still water is 10 km/hr. If covers upstream a distance of 45 km in 6 hours. The speed (in km/hr) of the stream is
(a) 2.5
(b) 3
(c) 3.5
(d) 4
3. A motorboat can run 18.5 km/hr in still water. If it covered 60 km upstream in 4 hours. Find the speed of current.
(a) 3
(b) 3.5
(c) 4
(d) 4.5
4. A motorboat, travelling at the same speed, can cover 25 km upstream and 39 km downstream in 8 hours. At the same speed, it can travel 35 km upstream and 52 km downstream in 11 hours. The speed of the stream is
(a) 2 km/hr
(b) 3 km/hr
(c) 4 km/hr
(d) 5 km/hr
5. A boat goes 12 km downstream and comes back to the starting point in 3 hours. If the speed of the current is 3 km/hr, then the speed (in km/hr) of the boat in still water is
(a) 12
(b) 9
(c) 8
(d) 6
6. A motor-boat can travel at 10 km/hour in still water. It travelled 91 km downstream in a river and then returned to the same place taking altogether 20 hours. Find the rate of flow of river.
(a) 3 km/hr
(b) 4 km/hr
(c) 2 km/hr
(d) 5 km/hr
7. The speed of the current is 5 km/hour. A motorboat goes 10 km upstream and back again to the starting point in 50 minutes. The speed, in km/hour, of the motorboat in still water is
(a) 20
(b) 26
(c) 25
(d) 28
8. A boat travels 24 km upstream in 6 hours and 20 km downstream in 4 hours. Then the speed of boat in still water and the speed of water current are respectively.
(a) 4 kmph and 3 kmph
(b) 4.5 kmph and 0.5 kmph
(c) 4 kmph and 2 kmph
(d) 5 kmph and 2 kmph
9. A boy can swim in still water at a speed of 10 km/hr. if the speed of the current would have been 5 km/hr, then the boy could swim 60 km.
(a) upstream in 4 hours
(b) downstream in 12 hours
(c) upstream in 6 hours
(d) downstream in 4 hours
10. Water is flowing at the rate of 5 km/h through a pipe of diameter 14 cm into a rectangular tank which is 50 m long, 44m wide. The time taken, in hours, for the rise in the level of water in the tank to be 7 cm is
(a) 2
(b) 1 ½
(c) 3
(d) 2 ½
Answers and Solution:
1. (b)
The speed of boat downstream = 15 + 5 = 20km/hr
so The distance downstream = speed downstream*time = 20*15/60 = 5km.
2. (a)
Let the speed of stream is x km/hr.
so the speed upstream = 10 - x km/hr
so The speed upstream*time = distance
so (10-x)*6 = 45
so x = 15/6 = 2.5 km/hr.
3. (b)
Speed downstream = 60/4 = 15 km/hr
so The speed of current = 18.5 - 15 = 3.5 km/hr
4. (c)
5. (b)
6. (a)
7. (c)
8. (b)
The speed downstream = 20/4 = 5 km/hr
The speed upstream = 24/6 = 4 km/hr
The speed of boat in still water = (5+4)/2 = 4.5 km/hr
The speed of current = (5-4)/2 = 0.5 km/hr
so The speed of boat and water current are 4.5 km/hr and 0.5 km/hr
9. (d)
speed downstream = 10+5 = 15 km/hr
speed upstream = 10-5 = 5 km/hr
so time taken to swim 60 km down stream = 60/15 = 4 hours
10. (a)
1. (b)
The speed of boat downstream = 15 + 5 = 20km/hr
so The distance downstream = speed downstream*time = 20*15/60 = 5km.
2. (a)
Let the speed of stream is x km/hr.
so the speed upstream = 10 - x km/hr
so The speed upstream*time = distance
so (10-x)*6 = 45
so x = 15/6 = 2.5 km/hr.
3. (b)
Speed downstream = 60/4 = 15 km/hr
so The speed of current = 18.5 - 15 = 3.5 km/hr
4. (c)
5. (b)
6. (a)
7. (c)
8. (b)
The speed downstream = 20/4 = 5 km/hr
The speed upstream = 24/6 = 4 km/hr
The speed of boat in still water = (5+4)/2 = 4.5 km/hr
The speed of current = (5-4)/2 = 0.5 km/hr
so The speed of boat and water current are 4.5 km/hr and 0.5 km/hr
9. (d)
speed downstream = 10+5 = 15 km/hr
speed upstream = 10-5 = 5 km/hr
so time taken to swim 60 km down stream = 60/15 = 4 hours
10. (a)
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