Boat And Stream

Q 9: The speed of a boat in still water is 5 km/hr. If its speed upstream be 2 km/hr then speed of the stream is A)3 km/hr B)5 km/hr C)1 km/hr D)8 km/hr Answer : Option A Explanation: Let the speed of stream be x km/hr Speed upstream = (5-x) km/hr => 5-x = 2 => x = 3 km/hr Q 10: Find the rate of the stream, if a boat covers 150 km downstream and 50 km upstream in 5 hours. A)10 km/hr B)15 km/hr C)20 km/hr D)8 km/hr Answer : Option A Explanation: Distance covered in downstream = 120 km Time taken in downstream = 4 hours. Rate of downstream = distance / time = a = 150 km / 5 hours = 30 km/hr. Distance covered in upstream = 50 km Since it takes same time to cover this 50 km, Time taken in upstream = 5 hours. Rate of upstream = distance / time = b = 50 km / 5 hours = 10 km/hr. Speed of stream = (a - b)/2 = (1/2)(30 - 10) km/hr = 10 km/hr. Q 11:If a boat goes 5 km upstream in 50 minutes and the speed of the stream is 3 km/hr, then the speed of the boat in still water is: A)8 km/hr B)5 km/hr C)9 km/hr D)None of these Answer : Option C Explanation: Rate upstream = (5/50)x 60 km/hr = 6 km/hr. Speed of stream = 3 km/hr. Let speed in still water is x km/hr Then, speed upstream = (x —3) km/hr. =>x-3 = 6 or x = 9 km/hr Q 12: The speed of a boat in still water is 12 km/hr and the rate of current is 2 km/hr. The distance travelled downstream in 8 minutes is : A)1.86 km B)2.85 km C)3.46 km D)5.86 km Answer : Option A Explanation: Speed downstream =(12 + 2)km/hr= 14 km/hr. Distance travelled = (14 x 8)/60 km = 1.86 km

« 1 2 3 »