8. A student was given the following problem: "The drawing shows a person (weight push-ups. Find the normal force exerted by the floor on each hand and each foot, as person holds this position." A. To find the answer, the student drew this Free Body Diagram. F, is the force on the hands, F, is the force on the feet and F, is the weight of the man. What is wrong with this diagram? B. After the student fixed the Free Body Diagram, they decided to solve the problem by putting the pivot point at the center of

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**Torques in Equilibrium (\(\Sigma \tau = 0; \tau_{cw} = \tau_{ccw}\))**

8. A student was given the following problem: "The drawing shows a person (weight, \(W=584\text{N}\)) doing push-ups. Find the normal force exerted by the floor on each hand and each foot, assuming that the person holds this position."

**A.** To find the answer, the student drew this Free Body Diagram. \(F_h\) is the force on the hands, \(F_f\) is the force on the feet and \(F_s\) is the weight of the man. What is wrong with this diagram?

**B.** After the student fixed the Free Body Diagram, they decided to solve the problem by putting the pivot point at the center of mass of the man. Why is this not a good idea?

**C.** The student next put the pivot point at the point where the feet touched the ground, but they were concerned because they wanted to calculate the torque: \(F \sin \theta\) but they weren't given any angles and weren't sure what to do. They don't need the angle for this problem, why?

**D.** Finally, the student wrote the following equation using the point where the feet touch the ground as the pivot point (they used \(\tau_{cw} = \tau_{ccw}\)):

\[
F_f (0.840 \text{ m}) = 2F_h (1.250 \text{ m})
\]

\[
F_f \times \frac{584\text{N}(0.840\text{ m})}{2(1.250\text{ m})} = F_h = 196\text{N}
\]

**E.** Now that we know the force on each hand, find the force on each foot.

---

The accompanying diagram shows a person doing push-ups with labeled distances and forces. The horizontal distances from the feet to the center of mass (0.840 m) and from the hands to the feet (1.250 m) are shown, indicating where the forces act.
Transcribed Image Text:**Torques in Equilibrium (\(\Sigma \tau = 0; \tau_{cw} = \tau_{ccw}\))** 8. A student was given the following problem: "The drawing shows a person (weight, \(W=584\text{N}\)) doing push-ups. Find the normal force exerted by the floor on each hand and each foot, assuming that the person holds this position." **A.** To find the answer, the student drew this Free Body Diagram. \(F_h\) is the force on the hands, \(F_f\) is the force on the feet and \(F_s\) is the weight of the man. What is wrong with this diagram? **B.** After the student fixed the Free Body Diagram, they decided to solve the problem by putting the pivot point at the center of mass of the man. Why is this not a good idea? **C.** The student next put the pivot point at the point where the feet touched the ground, but they were concerned because they wanted to calculate the torque: \(F \sin \theta\) but they weren't given any angles and weren't sure what to do. They don't need the angle for this problem, why? **D.** Finally, the student wrote the following equation using the point where the feet touch the ground as the pivot point (they used \(\tau_{cw} = \tau_{ccw}\)): \[ F_f (0.840 \text{ m}) = 2F_h (1.250 \text{ m}) \] \[ F_f \times \frac{584\text{N}(0.840\text{ m})}{2(1.250\text{ m})} = F_h = 196\text{N} \] **E.** Now that we know the force on each hand, find the force on each foot. --- The accompanying diagram shows a person doing push-ups with labeled distances and forces. The horizontal distances from the feet to the center of mass (0.840 m) and from the hands to the feet (1.250 m) are shown, indicating where the forces act.
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