Answer to Question #127334 in Physics for Lammo

Question

A boat whose speed is 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream is ___ km/hr.

Answer 1

$30/(15+x)+30/(15−x)=4.5$

$30(15−x)+30(15+x)=4.5⋅(225−x^2)$

$900=1012.5−4.5x^2$

$4.5x^2=112.5$

$x=5$ $km/hr$ Answer.