Problem 18: While exercising in a fitness center, a man lies face down on a benc
ID: 1775475 • Letter: P
Question
Problem 18: While exercising in a fitness center, a man lies face down on a bench and lifts a weight with one lower leg by contacting the muscles in the back of the upper leg. Part (a) Find the magnitude of the angular acceleration produced given the mass lifted is II kg at a distance of 29.5 cm from the knee joint the moment of inertia of the lower leg is 0.93 kgm2, the muscle force is 1400 N, and its effective perpendicular lever arm is 2.95 cm. Numeric A numeric value is expected and not an expression. Part (b) How much work is done if the leg rotates through an angle of 21.5° with a constant force exerted by the muscle? Numeric A numeric value is expected and not an expression net WExplanation / Answer
A)
Net torque = 1400N * 0.0295m - 11kg * 9.8m/s² * 0.295m
= 9.5 N·m
total I = 0.93kg·m² + 11kg*(0.295m)² = 1.887 kg·m²
= I
9.5 N·m = 1.887kg·m² *
= 5.03 rad/s²
B)
To find the work done, use the rotational equivalent of F*d:
work = * = 9.5 N·m * 21.5*/180 = 3.56 J
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