Final answer:
The triceps brachii muscle acts as an extensor when the arm is completely extended. In a physics problem, the moment of inertia of a boxer's forearm can be calculated using the torque generated by the triceps muscle and the known angular acceleration of the forearm.
Step-by-step explanation:
When you hold your arm out so that it is completely extended, the triceps brachii muscle is responsible for this action. The triceps brachii is acting as an extensor, which is a muscle that opens or extends a limb.
In the context of the physics involved, we can refer to a problem where this muscle in a professional boxer exerts a force of 2.00 × 10³ N with an effective perpendicular lever arm of 3.00 cm, producing an angular acceleration of the forearm of 120 rad/s². To calculate the moment of inertia of the boxer's forearm, we can use the formula τ = Iα, where τ is the torque, I is the moment of inertia, and α is the angular acceleration.
The torque here is the product of the force exerted by the triceps muscle and the perpendicular lever arm distance (r), which can be calculated as τ = (2.00 × 10³ N) × (3.00 × 10⁻² m) = 60 N·m. Using the angular acceleration of 120 rad/s², we can rearrange the formula to solve for I: I = τ/α = 60 N·m / 120 rad/s² = 0.5 kg·m², which is the moment of inertia of the boxer's forearm.