Answer:
a powerplay for the other team, and a penalty kill for the team with the player in the box
Explanation:
The initial kinetic energy of the cart is

(1)
where m is the mass of the cart and v its initial velocity.
Then, the cart hits the spring compressing it. The maximum compression occurs when the cart stops, and at that point the kinetic energy of the cart is zero, so all its initial kinetic energy has been converted into elastic potential energy of the spring:

where k is the spring constant and x is the spring compression.
For energy conservation, K=U. We can calculate U first: the compression of the spring is x=60 cm=0.60 m, while the spring constant is k=250 N/m, so

So, the initial kinetic energy of the cart is also 45 J, and from (1) we can find the value of the initial velocity:
The answer is 6... 14-8=6
Newton's 3rd law says that for every force there is an equal and opposite reaction force.
So for the force of the hammer hitting the nail, there is a force equal in magnitude exerted back on the hammer by the nail (and is "opposite" because it's in the other direction and on the hammer.)