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# M4 Relative Motion watch

1. A bird is capable of flying at 80Km/h . It wishes to fly to its nest which is due east of its present position. There is a wind blowing from the north-west at 70Km/h. Find the direction in which the bird must fly to reach its nest.
2. Draw a diagram.

You want to draw the birds resultant velocity vector and you want this to be going directly East. However, no matter which way the bird flies, he will be pushed South-East at 70km/h and since it doesn't matter in which order you add vectors to get the resultant, let's start by drawing on this 70km/h vector. Now the problem is saying...at what angle do I draw on the 80km/h vector such that the resultant is horizontal. Provided you know how to add two vectors it shouldn't be difficult.
3. (Original post by Spenceman_)
Draw a diagram.

You want to draw the birds resultant velocity vector and you want this to be going directly East. However, no matter which way the bird flies, he will be pushed South-East at 70km/h and since it doesn't matter in which order you add vectors to get the resultant, let's start by drawing on this 70km/h vector. Now the problem is saying...at what angle do I draw on the 80km/h vector such that the resultant is horizontal. Provided you know how to add two vectors it shouldn't be difficult.
Yeh, i mean i tried that, but i get the wrong anwser....??
4. Hmmm,

It seems that i have my diagram wrong. Is it possible if you can draw a quick diagram? I mean, i cant seem to draw it???
5. (Original post by Widowmaker)
|Vw| = 70
|Vb| = 80
ehrr....I just had a quick look again and i dont quite agree with the diagram. Shouldnt the velocity of the bird be towards east, and not the velocity of the bird relative to wind??

Because if this diagram is correct, then i dont understand why it is.
6. Apologise for the slight error. Misread the question.

Right. I've re-done the diagram.

|bVw| = 80
|Vw| = 70

=> 80/sin45 = 70/sin([email protected]) = 70/[email protected]
=> [email protected] = 70sin45
=> [email protected] = 70sin45/80
=> @ = 52 degrees
Attached Images

7. ahh!

Now it makes sence. Thanks.

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