Question

a motorboat whose speed is 12 km/hr in still water takes 2hours less to go 45km downstream than to return to upstream to the same spot find speed of curren.t

Answer 1

Answer:

Step-by-step explanation:

speed of boat=12

speed of current=c

upstream=speed of boat-speed of stream  =12-c

downstream=speed of boat+speed of water=12+c

dist=45km

sped =d/time

45/12-c  -  45/12+c ==2hrs

solving this we get

540+c - 540+c

----------------------    ===2

144-c^2

2c=288-c^2

c^2+2c-288=0

c^2+18c-16c-288=0                         (splitting middle term)

c(c+18) -16(c+18)

c=-18,16

-18 to be rejected as speed cannot be in negative terms

so,

speed of stream=16km/h

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Answer 2

Let the speed of the stream be x km\hr.

The speed of the boat upstream = (18 - x) km/hr

The speed of the boat downstream = (18 + x) km/hr

Distance = 24 km

As given in the question,

Time for upstream = 1 + Time for downstream

24/(18 - x) = 1 + 24/(18 + x)

24/(18 - x) - 24/(18 + x) = 1

x2 + 48x - 324 = 0

(x + 54)(x - 6) = 0

x ≠ - 54 as speed cannot be negative.

x = 6

The speed of the stream = 6 km/hr