21
Q:

A motorboat can go 10 miles downstream on a river in 20 min. It takes 30 min for this boat to go back at the same 10 miles. Find the speed of the current ?

A) 8 m/h B) 5 m/h
C) 7 m/h D) 6 m/h

Answer:   B) 5 m/h



Explanation:

As the distance travelled is constant, the time taken is inversely proportional to speed.

Let 'u' be the speed of the current and 'v' be the speed of the boat.

Speed of the boat downstream = v + u & upstream = v - u

=> v+u/v-u = 30/20 => v/u = 5 => v = 5u

=> v + u = 6u = 10/20/60 miles/hr

=> 6u = 30 m/h

=> u = 5 m/h

Q:

A boat covered a distance of 15 km upstream in 5 hours and a distance of 42 km downstream in 6 hours. The speed of the stream in km/h is:

 

 

A) 2 B) 3
C) 1.5 D) 2.5
 
Answer & Explanation Answer: A) 2

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3 713
Q:

A boat can cover a distance of 7.2 km downstream and 3.2 km upstream in 2 hours. It can also cover 1.5 km downstream and 0.6 km upstream in 24 minutes. What is the speed of the boat when going downstream (in km/h)?

 

A) 4.5 B) 6
C) 5 D) 7.5
 
Answer & Explanation Answer: B) 6

Explanation:
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4 646
Q:

A person can row a distance of 4 km upstream in one hour 20 minutes and can row back to the starting point in just 24 minutes. How much time(in hours) will he take to row 13 km in still water?

 

A) 2 B) 7/2
C) 3 D) 5/2
 
Answer & Explanation Answer: A) 2

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1 516
Q:

The speed of a motor boat in still water is 20 km/h .It travels 150 km downstream and then returns to the starting point. If the round trip takes a total of 16 hours, what is the speed (in km/h)of the flow of river?

 

 

A) 8 B) 6
C) 5 D) 4
 
Answer & Explanation Answer: C) 5

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4 690
Q:

The speed of a boat in still water is 12 km/h. If the boat covers a distance of 38 km upstream in 4 hours; then the speed of the stream (in km/h) is:

 

A) 6.5 B) 3.17
C) 2.5 D) 3
 
Answer & Explanation Answer: C) 2.5

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0 642
Q:

A boat can go 3.6 km upstream and 5.4 km downstream in 54 minutes, while it can go 5.4 km upstream and 3.6 km downstream in 58.5 minutes. The time (in minutes) taken by the boat in going 10 km downstream is:

 

A) 48 B) 50
C) 45 D) 54
 
Answer & Explanation Answer: B) 50

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1 1711
Q:

In a stream running at 3 km/h, a motorboat goes 12 km upstream and back to the starting point in 60 min. Find the speed of the motor boat in still water. (in km/h)

 

A) 2(2 + √17) B) 3(2 + √17)
C) 2(4 + √15) D) 3(4 + √17)
 
Answer & Explanation Answer: D) 3(4 + √17)

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3 1375
Q:

A boat at anchor is rocked by waves whose consecutive crests are 125 m apart. The velocity of the wave of the moving crests is 25 m/s. What is the frequency of the rocking of the boat?

A) 0.20 Hz B) 625 Hz
C) 250 Hz D) 100 Hz
 
Answer & Explanation Answer: A) 0.20 Hz

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2 1316