Motion in different reference frame

zorop · #1 $Old$ June 27th, 2009, 05:23 PM

This is a practice problem for the midterm, any advice and help would be awesome~ thanks everyone~

An airplane moves in a northwesterly direction a 125m/hr relative to the ground. due to the fact that there is a westerly wind (ie from west) of 50 m/hr relative to the ground. Determine how fast and in what direction the plane would have travelled if there were no wind.

Is this a simple question about the velocity combination like the net force in a triangle?
I am afraid that it should be more complicated for the midterm.

CaptainBlack · #2 $Old$ June 28th, 2009, 02:45 AM

Quote:

Originally Posted by zorop $View Post$

This is a practice problem for the midterm, any advice and help would be awesome~ thanks everyone~

An airplane moves in a northwesterly direction a 125m/hr relative to the ground. due to the fact that there is a westerly wind (ie from west) of 50 m/hr relative to the ground. Determine how fast and in what direction the plane would have travelled if there were no wind.

Is this a simple question about the velocity combination like the net force in a triangle?
I am afraid that it should be more complicated for the midterm.

Yes it is a simple velocity sum question:

$\bold{x}+50(-1,0)=\frac{125}{\sqrt{2}}(-1,1)$

Solve for vector $\bold{x}$ and then convert into speed and heading form.

CB

zorop · #3 $Old$ June 29th, 2009, 11:42 AM

thanks, i get it~ x = ((-125sqrt(2)+100)/2), 125sqrt(2)/2)
make x as a unit vector to find the speed and then get the angle as the direction~