Problem%20Set%2010%202009

# Problem%20Set%2010%202009 - Biomechanics IPHY 4540 Problem...

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Biomechanics IPHY 4540 Problem Set #10 Quiz on this material Monday, December 8 1. Work is measured in Joules which is defined as N m. Torque is measured in N m. Explain how work and torque are different even though the units seem to be the same. 2. A person is holding a weight (100 N) in their hand. The weight is a distance of 0.3 meters from the center of rotation of the elbow. a. If the forearm is parallel to the ground, what is the torque about the elbow due to the weight? b. If the forearm has an angle of 30° above the horizontal (hand is higher than elbow), what is the torque about the elbow due to the weight? c. If an elbow flexor muscle has a moment arm of 0.030 m about the elbow, what force must it generate to hold the forearm at an angle of 50° above the horizontal with the weight in the hand (ignoring the weight of the forearm)? 3. A person is wearing a weight boot (150N) and doing exercises to strengthen the knee extensor muscles. The center of mass of the weight boot is 0.35 meters from the center of rotation of the knee. The person's foot + shank has a weight of 40N and its center of mass is 0.2 meters from the center of rotation of the knee. These distances are along the length of the shank. a. When the shank is perpendicular to the ground, what is the total torque about the knee? (Be sure to use a free-body diagram.) b. When the shank is held at a position where it is 20° below the horizontal (foot is lower than knee), what is the torque about the knee? (Be sure to use a free-body diagram. Note that the moment arm of the weight boot about the knee changes with knee angle.) c. If the quadriceps muscle group has a moment arm of 0.025 m, what is the muscle force needed to hold the shank at 20° below the horizontal? 4. Obesity is an epidemic in the United States and it contributes to many metabolic and

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## This note was uploaded on 02/15/2010 for the course IPHY 4540 at Colorado.

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Problem%20Set%2010%202009 - Biomechanics IPHY 4540 Problem...

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