- #1

dl447342

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- Homework Statement
- The yoga exercise “Downward- Facing Dog” requires stretching your hands straight out above your head and bending down to lean against the floor. This exercise is performed by a 750 N person as shown in Fig. P11.67. When he bends his body at the hip to a 90° angle between his legs and trunk, his legs, trunk, head, and arms have the dimensions indicated. Furthermore, his legs and feet weigh a total of 277 N, and their center of mass is 41 cm from his hip, measured along his legs. The person’s trunk, head, and arms weigh 473 N, and their center of gravity is 65 cm from his hip, measured along the upper body.

(a) Find the normal force that the floor exerts on each foot and on each hand, assuming that the person does not favor either hand or either foot.

(b) Find the friction force on each foot and on each hand, assuming that it is the same on both feet and on both hands (but not necessarily the same on the feet as on the hands).

- Relevant Equations
- Equation for net torque: sum of ##\vec{r}\times \vec{F}## for all forces ##\vec{F}## and their position vectors.

Newton's first law; if an object is not accelerating, the net force on it must be zero.

I get how to solve (a); my method involves finding the net torque about the man's hands and setting it to zero, which can be used to solve for the normal force acting on his feet and the normal force on his hands can be solved using Newton's first law. Then divide by 2 for each to get the normal force on one hand or foot.

However, I'm not sure how to get part (b); neither setting the net torque about any point to 0 nor setting the net force to zero works because it seems the friction forces on his hands and feet are equal in magnitude and opposite in direction, so their torques about any point would always sum to zero.

https://www.ekhartyoga.com/media/im...ward-Facing-Dog-Pose-Adho-Mukha-Svanasana.jpg

However, I'm not sure how to get part (b); neither setting the net torque about any point to 0 nor setting the net force to zero works because it seems the friction forces on his hands and feet are equal in magnitude and opposite in direction, so their torques about any point would always sum to zero.

**[Image added by Mentors]**https://www.ekhartyoga.com/media/im...ward-Facing-Dog-Pose-Adho-Mukha-Svanasana.jpg

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