# Vectors Question using Calculus -- Swimmer crossing a River

jbriggs444
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2019 Award
View attachment 258490
Is this better?
That's the same drawing turned upside down.

You want the sum of the river velocity and the swimmer velocity to give a result that points directly across the river. Can you draw a right triangle to show that?

The flow velocity and the desired velocity are at right angles. If those are two of the sides of the triangle, it will indeed be a right triangle.

• PeroK
PeroK
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Gold Member
Who says it must be a right-angle triangle?
I meant, of course, why does the direction Bob's swims have to be at a right angle to the current?

A lot of my problems have right-angled triangles with them..
Is it not supposed to be a right angle?

PeroK
Homework Helper
Gold Member
A lot of my problems have right-angled triangles with them..
Is it not supposed to be a right angle?
As @jbriggs444 pointed out, it's the river's velocity and Bob's resultant velocity that you know are at right angles. Bob can swim at angle any relative to the river.

H
I meant, of course, why does the direction Bob's swims have to be at a right angle to the current?
He's swimming to the oppiste side.
As @jbriggs444 pointed out, it's the river's velocity and Bob's resultant velocity that you know are at right angles. Bob can swim at angle any relative to the river.
Relative meaning in the direction of.
I drew another diagram, I'm not sure if I'm on the right track.. etotheipi
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2019 Award
Relative meaning in the direction of.
I know this is an old thread, but this just bothered me. Relative to does not mean 'in the direction of', relative to implies a subtraction i.e. 'from the perspective of'. A part of a vector in a certain direction is something different, i.e. a vector component / vector projection.