- #1

in the rye

- 83

- 6

## Homework Statement

A boat propelled so as to travel with a speed of .5m/s in still water moves directly across a river that is 60m wide. The river flows with a speed of .3 m/s. At what angle relative to the straight across direction must the boat be pointed? How long does it take the boat to cross the river?

## Homework Equations

## The Attempt at a Solution

Okay, so my question really isn't on the math. It's on the question itself. I can solve it once I have a correct diagram. My question is, how do I draw my vectors? When they don't give details, I seem to frequently draw my resultant incorrectly. In this problem, I took the boats speed in still water to be directly across stream at .5 m/s considering it is moving "directly across the river." However, in the book, they take the boat in still water to be the resultant. Why? In fact, in reviewing my notes, my professor gave a similar example in which he took the "in still water" to mean the path directly from shore to shore if we consider our initial position to be the origin, it only moved one direction in his example. But the book does it differently and it screws upIt seems most of my issues are due more to reading comprehension or the way the problems are worded. I understand that directly can mean it is moving linear. However, if I told someone to walk directly across the street from our point of reference I wouldn't expect them to move diagonally across it. I would expect them to move in a horizontal straight line from the frame of reference where we are standing. Then, if there happens to be a strong wind that blows them right or left, the resultant would be from their vector walking directly from where there were plus the effects of the wind...

It's just frustrating that the most difficult part is just setting up the problems, and the way the text seems to do it just doesn't make any sense to me. When I have a diagram, or I am told angles, or direction, I can draw it perfectly and solve with no issues. But the moment there includes some sort of interpretation of the problem, I screw up. It doesn't matter how many examples I do. This keeps recurring.

I can kind of see how it may be inferred since you are getting the angle at which the boat must be pointed from the horizontal might mean that our "in still water" is the resultant vector, but I still think it's assuming that you want to go in the across stream direction

I need some help :/