How to Calculate Time and Displacement for a Ferry Boat Crossing a River?

[Wizzker]

Homework Statement

A ferry boat is crossing a river that is 8.5 x 10^2m wide. The average velocity of the waer relative to the shore is 3.8m/s (e) and the average velocity of the boat relative to the water is 4.9m/s (s).

Homework Equations

The Attempt at a Solution

So i got the first part down where it says to determine velocity of the ferry boat relative to the shore. I got 6.2m/s [E52*S].

part b) and c) is what i don't get.

b) How long does the crossing take?

c) Determine the displacement of the boat as it crosses from the north shore to the south shore.

Also another thing that confuses me is the velocities. Should it be for example water to shore, shore to boat, boat to water? Instead its like water to shore, boat to water, then it asks boat to shore. I don't know if its big deal but was just wondering because in examples in our book it has it going in order if that makes sense.

 

[Borek]

You have three vectors, given any two you can calculate third - so order doesn't matter.

You are given distance, you are given velocity, where is the problem with calculating time? I guess velocity of the boat relative to water is perpendicular to shore, which makes calculations pretty simple.