Lucku H.

asked • 11/11/15

Physics-trig question velocity of a plane etc HELP

A plane flies due north (90° from east) w/ a velocity of 110 km/h for 3 hours.A steady wind blows southeast at 35 km/h at an angle of 320 degrees from due east during this time. After 3 hours, where will the plane’s position be relative to its starting point?

I`m having trouble getting the answer I`ve started off with the formula v=sqrt{v(p)²+v(w)²-2v(p)v(w)cos α}
=sqrt(110²+35²-2*110*35cos45) = 88.8 km/h (rounded) Then did
s= vt=88.8*3=266.4 km
then tried getting the distance from the start by the following:
sqrt.(266.4^2 + 88. = 266.6 km N.E from starting point.
Although I have no idea why (trying to imitate a similar problem I did
this to get the angle from the start using tanL , L being the length
tanL = (266.6/88., which equals about degrees

Please explain . Agh thank you soo much

Mark M.

In my diagram I get the wind vector at 30° west of south of the direction of the plane.
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11/11/15

Bill K.

Why did you choose the angle in between the 2 vectors as 45° . I think it should be due north - 40 south of east (90 - 40 = 50° ).
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11/11/15

Hilton T.

tutor
You have used the law of cosine to find the magnitude of the resultant vector. When you draw a parallelogram of vectors, the correct angle should be 180- (90 + 40) = 50 degrees. If you use  cos 50 degrees in the law of cosine, you will end up with the correct magnitude.
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11/12/15

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