Near the edge of a roof of a 10 m high building, a person kicks a dough ball.
m= 500 g, with an initial velocity of 12 m/s at an angle of 30° above the horizontal. despising the
air resistance find: A) the mechanical energy of the ball when it reaches its maximum height. B) the speed
of the ball just before touching the ground. C) The kinetic energy of the ball when it reaches height
maximum, d) The work performed on the ball, from the highest point of the trajectory until immediately before
touching the ground.

The ball has to fall 10 meters. How long will it take to do that? Remember that the distance traveled under constant acceleration (such as gravity) is 1/2 at2 = 1/2 * 10t2 which has to equal 10 meters.

1/2 * 10 t2 = 10

5t2 = 10

t2 = 10/5 = 2

So the ball will take √2 seconds to fall.

During that time, it has to travel horizontally 10 meters. So the horizontal speed has to be 10/√2 m/s, so the answer is #1.