I already tried the methods from the solutions manual. I am doing this for an on

Question

I already tried the methods from the solutions manual. I am doing this for an online homework. This is what the Problem says :

A boat moves through the water of a river at
7.8 m/s relative to the water, regardless of the
boat’s direction.If the current is ?owing at 5.72 m/s, how
long does it take the boat to complete a trip
consisting of a 304 m displacement down-
stream followed by a 151 m displacement up-
stream?
Answer in units of s.

V of boat=VB= 7.8 m/s(regardless of direction)
V of current=VC= 5.72 m/s

and they are asking how long it takes that boat to travel
upstream= 304 m>>>> you have to find time for this (T1)
downstream=151 m>>>> you have to find time for this (T2)

VB (up) = VB-VC= 7.8-5.72= 2.08m/s is the velocity upstream
so to find the time upstream = 304m/2.08m/s =146.1538462 s= T1

VB(down) = VB+ VC= 7.8 + 5.72= 13.52 m/s
so to find the time downstream= 151m/13.52m/s = 11.16863905=T2

ROUNDTRIP =T1 + T2

when i plug in the sum of T1 AND T2 the answer is wrong. WHAT AM I DOING WRONG!!!!

Explanation / Answer

Ok real easy fix...The boat is going 7.8m/s relative to the water. So this velocity is the velocity of the boat (which is actually something bigger than 7.8) minus the velocity of the water. So VB(up) should be = 7.8 m/s. Because the question has already factored in the velocity of the water. hope that helps, if need clarification just ask.

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