Final answer:
The scientist is likely using the branch of physical science known as Mechanics to study the forces that act on a hockey puck.
Step-by-step explanation:
The branch of physical science that the scientist is likely using to study the forces that act on a hockey puck is Mechanics. Mechanics is the branch of physics that deals with motion, forces, and the behavior of physical objects. It involves studying concepts such as acceleration, velocity, friction, and Newton's laws of motion.