Question

The current of a stream runs at 5 kmph. A motor launch goes 25 km upstream and back again to the starting point in 275/2 minutes. The speed of the motor launch in the absence of any current is ​

Answer 1

Answer:

22.9 km/hr

Step-by-step explanation:

let say The speed of the motor launch in the absence of any current is = M km/hr

upstream speed = M-5 km/hr

time = 25/(M-5) hr

downstream speed = M+5 km/hr

time = 25/(M+5) hr

total time=275/2 mins

= 275/120 hr

25/(M-5) + 25/(M+5) = 275/120

5/(M-5) + 5/(M+5) = 11/24

120/(M-5) + 120/(M+5) = 11

120(M+5+M-5) = 11(M^2-25)

240M = 11M^2 - 275

11M^2 - 240M - 275 = 0

M = (240 + root(69700))/22

=22.9 km/hr