Ok, ive got a question. Its probably something really stupid that im overlooking, but ill ask anyway.(adsbygoogle = window.adsbygoogle || []).push({});

Say i have the question:

if a plane is can travel 75 m/s north (75ji assume?) under normal conditions, what velocity will the pilot need to set if he is to travel directly north when there are winds of 21i+8jm/s blowing.

Since i need to find the velocity which will make the plane travel at 75m/s north, 75jis therefore the resultant. If ai+bjis the velocity the pilot needs to set his engines at, i can say:

75j=ai+bj+21i+8j

I then equate the components, to get:

i0=a+21

j75=b+8

From that, i can solve for a and say that a=-21, and if i then substitute that into the equation:

[tex]75^2=(-21)^2+b^2[/tex]

solve for b and that gives me the velocity vector -21i+72j, which is the correct answer. What im wondering is, when i equated the components, i got two equations. When i used the first equation (0=a+21) and used the value of a to find the final vector, i get the correct answer, but when i used the value from solving b from 75=b+8, i get the wrong answer.

Thanks,

Dan.

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# Homework Help: Velocity Vector

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