Final answer:
The high bar exerts a force of 625.0 N upwards on the gymnast's hands, which is equal and opposite to the gymnast's weight due to gravity.
Step-by-step explanation:
The question asks about the force exerted by the high bar on a gymnast's hands when performing a handstand. In physics, particularly in the subsection of mechanics, there is a principle known as equilibrium which states that when a body is in static equilibrium, the sum of the forces and the sum of the torques on the body are zero. Since the gymnast is stationary and assuming he is not accelerating, the forces on him must be balanced. Therefore, the force the bar exerts on the gymnast's hands is equal and opposite to the gravitational force exerted on the gymnast by Earth.
In this case, the gymnast weighs 625.0 N, which is the gravitational force pulling the gymnast down towards the center of the Earth. By Newton's third law of motion, the high bar must exert an equal and opposite force to support the gymnast. Thus, the high bar exerts a force of 625.0 N upwards on the gymnast's hands.