Figure 12-29 shows the anatomical structures in the lower leg and foot that are

Question

Figure 12-29 shows the anatomical structures in the lower leg and foot that are involved in standing on tiptoe, with the heel raised slightly off the floor so that the foot effectively contacts the floor only at point P. Assume distance a = 6.5 cm, distance b = 19.5 cm, and the person's weight W = 630 N. Fig. 12-29

(a,b) What are the magnitude and direction of the force acting on the foot at point A from the calf muscle. (Include the sign. Take upward to be positive.) N

(c,d) What are the magnitude and direction of the force acting on the foot at point B from the lower leg bones? (Include the sign. Take upward to be positive.) N

Explanation / Answer

N = W/2 = 630/2 = 315 N

balancing moment about point B,

Fa x a - b x N = 0

Fa = 19.5 x 315 / 6.5 = 945 N .....Ans

upwards ...Ans

---------------

now balancing moment (r x F )about point A ,

(Fb x a) + (N x (a + b) ) = 0

Fb = - 315 x (6.5 + 19.5) / 6.5 = - 1260 N ........Ans

magnitude = 1260 N

direction = downwards

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