-- Mr. Galonski looks at himself in the mirror while he shaves in the morning, using visible light.
-- On his way to work, he listens to music and news, taking advantage of all the radio waves around.
-- While walking from his car to his office, he takes his jacket off and rolls up his sleeves, so his arms can soak up some ultraviolet from the sun, and get a little bit of color.
-- Mister Galonski is actually DOCTOR Galonski DDS ... a dentist. He uses a machine that produces X-rays, to take pictures of his patients' teeth and jaws. He glues the pictures into a big scrap-book that he keeps on the coffee table in his living room.
Answer:
The final velocity is 
Explanation:
From the question we are told that
The mass of the child is 
The initial speed of the child is 
The mass of the wagon is 
The initial speed of the wagon is 
The mass of the ball is 
The initial speed off the ball is 
Generally the initial speed of the system (i.e the child , wagon , ball) is

Generally from the law of linear momentum conservation

Here
is the momentum of the system before the ball is dropped which is mathematically represented as

=> 
=> 
and
is the momentum of the system after the ball is dropped which is mathematically represented as

=> 
So

=> 