- #1

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## Homework Statement

At noon, ship A is 150 km west of ship B. Ship A is sailing east

at 35 km

h and ship B is sailing north at 25 km

h. How fast is

the distance between the ships changing at 4:00 P.M.?

## Homework Equations

## The Attempt at a Solution

I did it using geometry and related rates and got 21.5 which was the answer

but I when I try to do it using relative velocity it doesnt work:

I am taking the first ship initial location as the origin

r

_{ai}=0

r

_{bi}=150i

r

_{a}=0+35ti

r

_{b}=150i+25tj

ra/b=a/g +ag/b

ra/b=0+35ti - 150i+25tj

ra/b=(35t-150)i + 25tj

dr(a/b) /dt = 35i+25j

and the magnitude is the way more than 21.5

I feel like I am doing something really wrong or setup the problem wrong.