Motion in 2 Directions: An Algebraic Approach

[gungo]

Homework Statement

A swimmer jumps into a 5.1 km river and swims straight to the other side at 0.87 km/h [N].
There is a current in the river of 2.0 km/h [W]
a)How long does it take the swimmer to reach the other side?
b)How far downstream has the current moved her by the time she reaches the other side?

Homework Equations

v= d/t
a^2+b^2=c^2

The Attempt at a Solution

a) I got the correct answer but I don't understand why the 0.87 km/h [N] was used instead of the 2.0 km[W]
t=d/v
t=5.1/0.87
t=5.9 hrs
b) total velocity= √0.87^2+2^2
=2.18
I'm really not sure what I'm trying to look for??

 

[alveeno]

Your answer to Part A was correct because motion in the X direction is independent of motion in the Y direction.
As the swimmer swims to the other side, you're given the swimmer's speed as she swims across. The current of the river doesn't affect the time it takes for the swimmer to reach the other side.

For Part B, you want how far she's been taken down stream during the time it took for her to reach the other side, or delta X.
Let me know if you have any other questions.