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10 May 2018

9.82 - BIO The Kinetic Energy of Running. Using Problem 9.81 as a guide, apply it to a person running at 12 km/h, with his arms and legs each swinging through 30° in s. As before, assume that the arms and legs are kept straight.

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Beverley SmithLv2
12 May 2018
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Physics: Principles with Applications
7th Edition, 2013
Giancoli
ISBN: 9780321625922

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9.81 - BIO The Kinetic Energy of Walking. If a person of mass M simply moved forward with speed V, his kinetic energy would be MV. However, in addition to possessing a forward motion, various parts of his body (such as the arms and legs) undergo rotation. Therefore, his total kinetic energy is the sum of the energy from his forward motion plus the rotational kinetic energy of his arms and legs. The purpose of this problem is to see how much this rotational motion contributes to the person's kinetic energy. Biomedical measurements show that the arms and hands together typically make up 13% of a person's mass, while the legs and feet together account for 37%. For a rough (but reasonable) calculation, we can model the arms and legs as thin uniform bars pivoting about the shoulder and hip, respectively. In a brisk walk, the arms and legs each move through an angle of about 30° (a total of 60°) from the vertical in approximately 1 second. Assume that they are held straight, rather than being bent, which is not quite true. Consider a 75-kg person walking at 5.0 km/h, having arms 70 cm long and legs 90 cm long. (a) What is the aver- age angular velocity of his arms and legs? (b) Using the average angular velocity from part (a), calculate the amount of rotational kinetic energy in this person's arms and legs as he walks. () What is the total kinetic energy due to both his forward motion and his rotation? (d) What percentage of his kinetic energy is due to the rotation of his legs and arms?

9.81 - BIO The Kinetic Energy of Walking. If a person of mass M simply moved forward with speed V, his kinetic energy would be MV. However, in addition to possessing a forward motion, various parts of his body (such as the arms and legs) undergo rotation. Therefore, his total kinetic energy is the sum of the energy from his forward motion plus the rotational kinetic energy of his arms and legs. The purpose of this problem is to see how much this rotational motion contributes to the person's kinetic energy. Biomedical measurements show that the arms and hands together typically make up 13% of a person's mass, while the legs and feet together account for 37%. For a rough (but reasonable) calculation, we can model the arms and legs as thin uniform bars pivoting about the shoulder and hip, respectively. In a brisk walk, the arms and legs each move through an angle of about 30° (a total of 60°) from the vertical in approximately 1 second. Assume that they are held straight, rather than being bent, which is not quite true. Consider a 75-kg person walking at 5.0 km/h, having arms 70 cm long and legs 90 cm long. (a) What is the aver- age angular velocity of his arms and legs? (b) Using the average angular velocity from part (a), calculate the amount of rotational kinetic energy in this person's arms and legs as he walks. () What is the total kinetic energy due to both his forward motion and his rotation? (d) What percentage of his kinetic energy is due to the rotation of his legs and arms?

I tried to solve this problem twice but i can't get the rightresults.

If a person of mass M simply moved forward with speed V, hiskinetic energy would be 1/2MV2 . However, in addition topossessing a forward motion, various parts of his body (such as thearms and legs) undergo rotation. Therefore, his total kineticenergy is the sum of the energy from his forward motion plus therotational kinetic energy of his arms and legs. The purpose of thisproblem is to see how much this rotational motion contributes tothe person's kinetic energy. Biomedical measurements show that thearms and hands together typically make up 13.0% of a person's mass,while the legs and feet together account for 37.0% . For a rough(but reasonable) calculation, we can model the arms and legs asthin uniform bars pivoting about the shoulder and hip,respectively. In a brisk walk, the arms and legs each move throughan angle of about ±30o (a total of 60o ) fromthe vertical in approximately 1 second. We shall assume that theyare held straight, rather than being bent, which is not quite true.Let us consider a 75.0 person walking at 5.00km/h having arms70.0cm long and legs 90.0cm long.

A)What is the average angular velocity of his arms and legs?

B)Using the average angular velocity from part A, calculate theamount of rotational kinetic energy in this person's arms and legsas he walks.

C)What is the total kinetic energy due to both his forwardmotion and his rotation?

D)What percentage of his kinetic energy is due to the rotationof his legs and arms?

If you want to help, you don't need to solve the whole problem.Just explain how to solve. If you understand or know how to solvethis problem, please help.

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