To develop muscle tone, a woman lifts a 2.4 kg weight held in her hand. She uses her biceps muscle to flex the lower arm through an angle of 21°. What is the instantaneous angular acceleration if she starts her workout with her arm vertical in the downwards direction? Assume the weight is 29 cm from the elbow joint, her forearm has a moment of inertia of 0.245 kg⋅m2, and the muscle force is 850 N at an effective perpendicular lever arm of 1.7 cm in rad/s2.