A 20-kg child is coasting at 3.3 m/s over flat ground in a 4.0-kg wagon. The child drops a 1.0-kg ball out the back of the wagon. What is the final speed of the child and wagon?

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

=>  

5 w for 1hr = 5x60x60 joules=300x60=3000x6=18,000j as total energy conversion. efficiency of bulb needed for radiant to thermal within 18000