A boat downstream from A to B takes 7 hours, upstream from B to 9 hours. How much time does a log take from A to B? (Driftwood along the water velocity)
1 Answer
The log will make the trip from A to B in 63 hrs.
Explanation:
Let s be the distance from A to B, the velocity of the river be
Analyse downstream travel:
The distance
#s = (v_b + v_r)*7 hrs#
Analyse downstream travel:
The distance
#s = (v_b - v_r)*9 hrs#
We have 2 expressions for s, so we can say that those 2 expressions are equal to each other.
Let's simplify that and solve for
The floating log will travel at the velocity
That relationship can be rewritten
That says that
I hope this helps,
Steve