An athlete of height 1.7 m and mass 50 kg does pushups. Her center of mass is 1.

Question

An athlete of height 1.7 m and mass 50 kg does pushups. Her center of mass is 1.0 m from her feet and her palms are at a distance of 30 cm from her head. She is in an instantaneously static position when her body is i) horizontal (contact only at feet and hands) and ii) when her body her arms are extended vertically by 50 cm. In each case, estimate the forces on each of her hands and feet. In each case assume that she pivots about her ankles, and that her feet are vertically oriented with a distance from floor to ankle of 15 cm.

Explanation / Answer

While stationary, the total moment about an axis through her toes is zero.

Her hands are 1.7 m from her toes. Her center of mass is 1.0 m from her toes.

F*1.7 - M*g*1.0 = 0

F = (1/1.7)M*g = 294.1 Newtons

Same will be in second case also as the center of gravity will also move vertically by 50 cm. hence net force in second case also will be 294.1 Newtons

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