First, assume that the arrow leaves the bow with a velocity of 45 m/s above the horizontal with respect to the bow.
Since the bow is moving at 8.5 m/s 45º below the horizontal, find the initial velocity of the arrow with respect to the ground:
This equation reads:
<em>The velocity of the arrow with respect to the ground </em><em>is equal to</em><em> the velocity of the arrow with respect to the bow </em><em>plus</em><em> the velocity of the bow with respect to the gound.</em>
Notice that this is a vector equation. Then, the vertical and horizontal components of the velocities must be added separately:
Find the vertical and horizontal components of the velocity of the arrow with respect to the bow and the velocity of the bow with respect to the ground:
Similarly, for the velocity of the bow with respect to the ground:
Then, the vertical and horizontal components of the initial velocity of the arrow with respect to the ground, are:
Use the horizontal component of the velocity to find how long it takes for the arrow to travel a horizontal distance x of 55 meters. Then, use that time to find the vertical position of the arrow.
Since the horizontal movement of the arrow is uniform, then:
Isolate t and substitute x=55m, v_{AG-x}=44.98 m/s:
The vertical motion of the arrow is a uniformly accelerated motion. Then, the vertical position is given by:
Replace v_{AG-y}=16.49 m/s, t=1.2227s and g=9.81 m/s^2 to find the vertical position of the arrow when the horizontal position is 55 meters. This matches the elevation of the dragon with respect to the girl when the girl shoots:
Therefore, the dragon is 12.8 meters above the girl when the arrow is shoot.