The Achilles tendon force of F_t=650 N is mobilized when the man tries to stand on his toes. As this is done, each of his feet is subjected to a reactive force of N_f=400 N. Determine the resultant moment of F_t and N_f about the ankle joint A.
Image from: Hibbeler, R. C., S. C. Fan, Kai Beng. Yap, and Peter Schiavone. Statics: Mechanics for Engineers. Singapore: Pearson, 2013.
Solution:
Let us write a moment equation about point A. We will assume clockwise moments to be positive.
\circlearrowright M_A=(650\cos5^0)(0.065)-(400)(0.1)
M_A=2.09\,\text{N}\cdot\text{m}\circlearrowright\text{(Clockwise)}
M_A=2.09\,\text{N}\cdot\text{m}\circlearrowright\text{(Clockwise)}