Kite is  ft above the ground.

Kite moves horizontally at a speed of  ft/s.

Assume that kite be at the point  and string on the ground at the point .

Assume horizontal distance between the kite and ground is .

Length of the string is .

Speed of the kite is  ft/s.

Consider .

Find the horizontal distance from kite to the string.

Consider

Substitute  in above expression.

Find the relation between the horizontal distance and height:

Consider .

Differentiate on each side with respect to .

Substitute  ,  and  in above expression.

Here the negative sign indicates angle is decreasing.

Rate at which angle between the string and the horizontal decreasing is               rad/s.

Rate at which angle between the string and the horizontal decreasing is                rad/s.