The area of a triangle is found by multiplying the height of the triangle by the length of the base and dividing them both by 2. The length of the shorter side in the equation is useless information, so just multiply 39 by 25 and divide that by 2. A=487.5 sq ft. Also, that's a pretty big kite.
Build walls around the coast
-- Energy is never created or destroyed.
-- No energy is added to the pendulum during its swing.
-- If we ignore air resistance and friction, then no energy is lost
from the pendulum during its swing.
-- Therefore the total energy of the pendulum must be constant.
-- Any potential energy lost at any point in the swing
must show up as kinetic energy. If it had 484J at the top,
then it'll have 484J at the bottom.
50km / 2.5 = 20 km per hour
