# Homework Help: Calculate force from wind on kite

1. Feb 3, 2012

### getty102

1. The problem statement, all variables and given/known data

A large kite of mass 3.8kg is flying through the air on a windy day. Currently, the tension from the string on the kite has a magnitude of 8.7N at an angle θ=33.7 degrees. The current acceleration of the kite has a magnitude of a=6.28m/s/s at an angle $\Phi$=38.7 degrees. The only forces felt by the kite are its own weight, the tension from the string, and a foce from the wind. Find x-component of the force from the wind on the kite. The components of a are acos$\Phi$ in the negative x-direction, and asin$\Phi$ in the positive y-direction.

2. Relevant equations
ƩF=ma for the x and y directions

3. The attempt at a solution
ƩFx=m(acos$\Phi$)
FTsinθ-Fx,WKcos$\Phi$=m(acos$\Phi)$)
Fx,WK=[-m(a)+FTsinθ]/cos$\Phi$

This doesn't seem to be working

2. Feb 4, 2012

### BruceW

FTsinθ-Fx,WKcosΦ=m(acosΦ))

Here, you don't need to multiply Fx,WK by cosΦ because the fact that it is the x component 'takes into account' the angle of the wind force, if you see what I mean. Also, the angle wouldn't be the same as the angle of the acceleration of the kite anyway.

Also, you wrote: ƩFx=m(acosΦ) But it says in the question that the component of a in the negative x direction is acosΦ, so shouldn't there be a negative sign here?

Another possible reason that you might have the wrong answer is that you might have interpreted the angles wrong. I can't tell, because I don't know where the angles are being measured from / what direction, since I don't have the diagram.