Problema Solution
A river is flowing downstream at a rate of 2 metres per second. Brendan, who has an average swimming speed of 3 metres per second, decides to go for a swim in the river. He dives into the river and swims downstream to a certain point then swims back upstream to the starting point. The total time taken is 4 minutes. How far did Brendan swim downstream?
Answer provided by our tutors
let
v = 3 m/s the swimming speed of Brendan
c = 2 m/s the speed of the stream
t1 = the time of the swim downstream
t2 = the time of the swim upstream
the total time taken is 4 minutes = 240 sec
t1 + t2 = 240
swimming downstream the speed of Brendan is v + c
swimming upstream the speed of Brendan is v - c
since he swims the same distance up and down we can write
(v + c)*t1 = (v - c)t2
(3 + 2)t1 = (3 - 2)t2
5t1 = t2
by solving the system of equations
t1 + t2 = 240
5t1 = t2
we find
t1 = 40 sec
t2 = 200 sec
click here to see the step by step solution of the system of equations
distance = 5*40 = 200 meters
Brendan swam 200 meters downstream.