Solving Statement For Upstream And Downstream


 
 
Concept Explanation
 

Solving Statement For Upstream And Downstream

In these type of situations, while calculating upstream speed we subtract the speed of river from the speed of boat because the river is pushing the boat downwards even when the boat is moving upwards. Whereas when the boat is moving downstream the speed is calculated by adding the speed of river to the speed of boat.

 

Let the speed of a boat ( or a body) in still water be x km/h and that of stream be y km/h, then

  • Speed of boat downstream = (x +y ) km/h
  • Speed of boat upstream = ( x - y) km/h
  • Let the speed of boat in downstream and upstream be u km/h and v km/h, then

    Speed of boat in still water

    =frac{1}{2}(u-v)km/h

    Illustration: A boat goes downstream from one point to another in 9 hours. It covers the same distance upstream in 10 hours. If the speed of the stream is 1 km/hr. Calculate the speed of boat in still water.

    A. 15 Km/h          B. 7.5 Km/h          C. 19 Km/h           D. 7 Km/h

    Answer: C

    Solution:     Let the speed of boat in still water be x km/hr

    Speed of stream  = 1 km/hr

    Speed upstream = x - 1 km/hr

    Speed Downstream = x + 1 km/hr

    As we know

     large speed= frac{distance}{time}

    Rightarrow distance= speed; X ;time

    Distance upstream = (x-1) X 10 = 10x - 10 Km

    Distance Downstream = (x+1) X 9 = 9x + 9 Km

    According to the question the distance is the same

                              10x-10 = 9x + 9

                              10x - 9x = 9+ 10

                                        x = 19 km/hr

    So the speed of boat in still water = 19 km/h

    Hence the correct option is C.

    Illustration: A motor boat whose speed in still water is 15 km/h, goes 40 km down stream and comes back in a total time of 6 hours. Find the speed of stream.

    A. 5 Km/h          B. 6 Km/h          C. 15 Km/h           D. 7 Km/h

    Answer: A

    .... (More Text Available, Login?)
    Sample Questions
    (More Questions for each concept available in Login)
    Question : 1

    The speed of a motorboat is 30 km/h. It starts from Mumbai at 6 am and reaches Goa at 8 am. Same day, it  starts from Goa at 12 pm and reaches Mumbai at 4 pm. Find the speed of stream.

    Right Option : C
    View Explanation
    Explanation
    Question : 2

    The current of a stream runs at 1 km/h. A motorboat goes 35 km upstream and back again at the starting point in 12 h. What is the speed of motorboat in still water ?

    Right Option : C
    View Explanation
    Explanation
    Question : 3

    A boat goes downstream from one point to another in 12 hours. It covers the same distance upstream in 15 hours. If the speed of the stream is 1 km/hr. Calculate the speed of boat in still water.

    Right Option : B
    View Explanation
    Explanation
     
    Video Link - Have a look !!!
     
    Language - English
     
     
     
     


    Students / Parents Reviews [20]