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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.
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Added Wed, 01 Jul '15
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Let F1 be the upward force which the floor exerts on his feet; and F2 be the upward force which the floor exerts on his hands.

Weight = 81 * 9.8 = 793.8
F1 + F2 = 793.8

The distance from his feet to his center of mass is 1.15 m. The distance from his feet to the centers of his palms is 2 � 0.30 = 1.7 m

Counter clockwise torque = 793.8 * 1.15 = 912.87

Clockwise torque = F2 * 1.7
F2 * 1.7 = 912.87
F2 = 912.87 � 1.7 =536.98N

F1 = 793.8 � (912.87 � 1.7) = 256.81 N

force exerted by floor on each of his feet= F1/2 =     128.53 N ( answer)

force exerted by floor on each of his hand = F2/2=   268.765N   (answer)
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