# Homework Help: Relative motion problem

1. Jan 22, 2008

### temaire

1. The problem statement, all variables and given/known data
http://img221.imageshack.us/img221/5571/kinematicslz1.jpg [Broken]
I asked my teacher to clarify this question a bit more, and she said that the man wanted to end up exactly opposite to where he was on the west shore, or in other words, parallel to where he was from the east shore.

2. Relevant equations
soh cah toa
$$a^{2} + b^2 = c^2$$

3. The attempt at a solution
I think that the answer is B), because in order for him to end up exactly opposite of where he is, he must go west.
However, my teacher thinks that the answer is D). Who's right?

Last edited by a moderator: May 3, 2017
2. Jan 22, 2008

### temaire

Can anyone help?

3. Jan 22, 2008

### awvvu

If he goes straight west, he won't land directly opposite of his starting position, since the river will have pushed him north. Therefore he must travel at some angle south of west.

4. Jan 22, 2008

### temaire

Sorry, I meant to say that the man wanted to go straight west, so he had to go 10kkm/h at an angle. But the question is asking for the actual velocity, or in other words, the ground velocity, which is, as I think, 8.0 km/h west.

5. Jan 22, 2008

### awvvu

Yes, I suppose it depends on your interpretation of the question then.

6. Jan 22, 2008

### temaire

Well it says actual motion.