To strengthen his arm and chest muscles, an 81.0kg athlete 2.00m tall is doing a

Question

To strengthen his arm and chest muscles, an 81.0kg athlete 2.00m tall is doing a series of push-ups as shown in the figure below (Figure 1) . His center of mass is 1.15m from the bottom of his feet, and the centers of his palms are 30.0cm from the top of his head. Find the force that the floor exerts on each of his feet and on each hand, assuming that both feet exert the same force and both palms do likewise.

Part A

Find the force that the floor exerts on each of his feet, assuming that both feet exert the same force.

Part B

Find the force that the floor exerts on each of his hand, both palms exert the same force.

Explanation / Answer

this can be solved by equating the forces and the moments.

equating forces gives us;

81g=Fl + Fh

where Fl is the reaction force on both the legs and Fh is for the hands

now take net moment about the cg which is equal to zero;

Fl * 1.15 = Fh * 0.55

Fl=0.48 * Fh

so,

0.48Fh + Fh=81g

Fh=54.72g=536.89N

Fl=81g-Fh=257.72N

So each leg gets a force of 257.72/2=128.86N

Each hand gets a force of 536.89/2=268.445N

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