Exercise 11.15 To strengthen his arm and chest muscles, an 85.0kgathlete 2.00m t
ID: 1382426 • Letter: E
Question
Exercise 11.15
To strengthen his arm and chest muscles, an 85.0kgathlete 2.00m tall is doing a series of push-ups as shown in the figure below (Figure 1) . His center of mass is 1.10m 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
A)
Let F_feet is the force exerted by floor on each feet
and F_palm is the force exerted by floor on each palm.
Net torque about his palm is zero.
M*g*(0.9 - 0.3) - 2*F_feet*1.7 = 0
85*9.8*0.6 - 2*F_feet*1.7 = 0
==> F_feet = 85*9.8*0.6/(2*1.7)
= 147 N <<<<<<<<<-------------Answer
B)
Net torque about his feet is zero.
-M*g*1.1 + 2*F_palm*1.7 = 0
-85*9.8*1.1 - 2*F_palm*1.7 = 0
==> F_palm = 85*9.8*1.1/(2*1.7)
= 269.5 N <<<<<<<<<-------------Answer
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