# Rowing across a river

1. Jan 15, 2014

### negation

1. The problem statement, all variables and given/known data

You wish to row straight across a 63m wide river. You can row at a steady 1.3 m/s relative to the water, and the river flows at 5.7 m/s. In what direction should you head? How long will it take you to cross the river?

3. The attempt at a solution

Last edited: Jan 15, 2014
2. Jan 15, 2014

### phinds

Think about this with simple logic for a minute. The river is flowing downstream at some speed. In order to not be at all swept downstream, the upstream component of your rowing speed relative to the river has to exactly match the downstream speed of the river. Is that possible in this problem?

3. Jan 15, 2014

### negation

4. Jan 15, 2014

### phinds

Are you going to answer my question or just continue to ignore it?

5. Jan 15, 2014

### negation

I've already answered it. In rowing at 116° from the x-axis, the boat goes against the current, no?

6. Jan 15, 2014

### negation

I tried solving it from another approach, where;

(1.3ms^-1)^2 = (0.57ms^-1)^2 +y^2
y = 1.168ms^-1
theta = 26°

7. Jan 15, 2014

### phinds

You need to reread my question in post #2. You have not answered it.

8. Jan 15, 2014

### haruspex

There's a typo in the OP. If you look at the attachment you'll see the river speed is given as 0.57 m/s.
Yes, negation, the answer is 26 degrees to the normal.

9. Jan 15, 2014

### phinds

Ah ... well that explains it.

10. Jan 15, 2014

### negation

My mistake for the typo. I apologize.
Would that be the same as 116 degrees from the x-axis since it would in other words implies 26 degrees NW.

Edit: I think it is.

11. Jan 15, 2014

### negation

It's not possible since
v_downwards> v_upwards.
I made a typo in the values.

12. Jan 15, 2014

### haruspex

Since the OP says nothing about x or y axes, nor about compass directions, that's impossible to answer.
In terms of river bank and direction of flow of river, where were you measuring 116 degrees from?

13. Jan 15, 2014

### negation

I measured 116° from the x-axis.
That would put the boat in quadrant 2 but of course since there was no reference point mentioned by the question, it could equally be implied 26° NW, 64° from the x-axis or 26° NE, isn't it?
I have a preference for 116° from the x-axis to do away with all the bearings.

14. Jan 15, 2014

### haruspex

I cannot see inside your head. I do not know where your x axis is, nor which way the river runs in terms of a compass bearing.

15. Jan 15, 2014

### negation

There.

16. Jan 16, 2014

### haruspex

17. Oct 27, 2015

### Mahmood Abd

How long will it take?
t=d/v
t=63/1.3=48.5 s
is it correct?
i am comfused since the answer in my textbook tells that t=53.9 s.