Question

animals that can run fast tend to have thin legs close to their pivotal axis. their leg muscles are concentrated close to the hip joint; only tendons extend into the lower leg. using the concept of rotational inertia, explain how this helps them run fast. multiple choice thin legs are lighter, reducing the overall weight of the animal. concentrating mass closer to the hip joint maximizes rotational inertia, allowing for faster leg swings. concentrating mass closer to the hip joint reduces rotational inertia, allowing for faster leg swings. less muscle mass in the lower leg reduces air drag which allows the animals to sprint faster.

Explanation:

Rotational inertia ($I = \sum mr^2$) depends on mass distribution. Concentrating mass near the hip (axis) reduces $r$ for leg mass, lowering $I$. Lower $I$ means less torque is needed for angular acceleration, enabling faster leg swings (key for running fast), matching the animal's anatomy. Other options: A (overall weight not rotational inertia), B (maximizing $I$ slows motion), D (air drag unrelated to rotational inertia here).

Answer:

C. Concentrating mass closer to the hip joint reduces rotational inertia, allowing for faster leg swings.