In vertical motion the arrow will be accelerating so we can use equation of motion
but first we need to find initial vertical and horizontal velocity
Horizontal velocity
cos65=x( horizontal)/20
x=8.45m/s
Thus now we can calculate time after which it strike the wall
8.45=10/t
t=1.18 s this speed in horizontal will remain constant
vertical intial velocity
sin65=y(vertical)/20
y=18.13 m/s
use the equation of motion to calculate height
s=ut+1/2 at^2
s=(18.13)(1.18)+ 1/2 (-9.8)(1.18^2)
s=21.40-6.822
s=14.58 m
but as it is already 1.80 above ground
So
The height of wall be =14.58+1.80=16.38m
ANSWER 16.38 meters
