The person whose leg is shown in Figure 10.20 kicks his leg by exerting a 2000-N force with his upper leg muscle. The effective perpendicular lever arm is 2.20 cm. Given the moment of inertia of the lower leg is 1.25 kg m²,

(a) Find the angular acceleration of the leg. 

(b) Neglecting the gravitational force, what is the rotational kinetic energy of the leg after it has rotated through 57.3° (1.00 rad)?

Strategy

The angular acceleration can be found using the rotational analog to Newton’s second law, or The moment of inertia І is given and the torque can be found easily from the given force and perpendicular lever arm. Once the angular acceleration α is known, the final angular velocity and rotational kinetic energy can be calculated.

Transcribed Image Text:

Femur F r₁= 2.20 cm 1 = 1.25 kg•m²