How should a bird adjust its direction to fly north in a crosswind?

[Peter G.]

So, I started my I.B Course for Physics High and we've took off with a simple subject, addition of vectors. We finished it today but the last question was quite hard. I had a try, asked the teacher but the thing is I can't understand what the problem asks for, or how to approach the problem:

A bird flies at a steady speed of 3 m/s through the air. It is pointing in the direction due north. However, there's a wind blowing from west to east at a speed of 2 m/s. It then asked for the resultant velocity and displacement which I handled with no problem and finished off with: In what direction should the bird point if it is to travel in a northerly direction?

So, firstly: By northerly, should the resultant velocity direction be bearing 0? Like, straight line, north? Or the bird should move towards the north direction?

So, the teacher put the answers up the board so after I had a try I looked. From the answer, I managed to reproduce the diagram obviously and identify the angle but I still don't understand the question itself

Sorry, I don't know how to post up the picture but in case you guys find it helpful:
tap.iop.org/mechanics/statics/file_39599.doc

Last question, both answer and question available.(3)

Thanks in advance,
Peter G.

 

[verty]

I think the problem is the problem. I mean, the problem is a bit confusing. It asks for displacement, but we are only given two velocities. One can get the resultant velocity, which I hope you know how to do, but one can't get a displacement, only a rate of displacement (which is just velocity).

So ignoring the question of displacement, determining the resultant velocity you know how to do. The second part is almost the same. Now the resultant velocity must face north. The bird must fly north and a little west, to counter the effect of the wind. How much west must the bird fly? Just enough, that is the clue. Draw a sketch, put in the magnitudes and use your knowledge of trigonometry to find the answer.

 

[Peter G.]

Ah, ok, so the resultant velocity is towards north. For example (this will be a bit confusing). The counter effect of the wind will be 2ms west. I draw one arrowed line towards my left. I draw a North Line, upwards (my resultant direction) and join a 3ms line from the 2ms line to the North line.

Yeah, to know the displacement we would need to know for how long he flew and multiply by our resultant velocity.

Thanks,
Peter G

 

[verty]

You got it. Then draw an accurate scale diagram to measure the angle or use trigonometry, whichever is easier. The answer would be something like 20 degrees W of N, or whatever.