As per momentum conservation we can say that Chuck and ball as a system has no external force
So here momentum of them must be conserved
now here initially if they are at rest
so we can say


now we have

now the relative velocity of the cart and ball is given as

also we can say since they are moving in opposite direction so relative speed will be

Answer:
90J
Explanation:
The only time work is being done is when he lifts the box off the ground. Therefore, using the work formula, 2 x 45, you get 90J. Hope this helps someone.