When you stand on your tiptoes, your feet pivot about your ankle As shown in the
ID: 3163916 • Letter: W
Question
When you stand on your tiptoes, your feet pivot about your ankle As shown in the figure, the forces on your fool are an upward force on you' toes from the floor, a downward force on your ankle from the lower leg bone, and an upward force on the heel of your foot from your Achilles tendon (Figure 1) Suppose a 51 kg woman stands on tiptoes with the sole of her foot making a 25 angle with the floor. Assume that each foot supports half her weight. Part A What is the upward force of the floor or the toes of one foot? The Young's modulus of the tendon is 0.15 times 10^10 N/m^2. 120 N 250 N 360 N 500 N Part B What upward force does the Achilles tendon exert on the heel of her foot? 250 N 360 N 500 N 750 N Part C The tension in the Achilles tendon will cause it to stretch. If the Achilles tendon is 15 cm long and has a cross-section area of 110 mm^2, by how much will it stretch under this force? 0.02 mm 0.7 mm 2.3 mm 5.2 mmExplanation / Answer
a) upward force of the floor on the toes of one foot = 51/2 * 9.8
= 249.9 N = 250 N
Option B is correct
b) Here, downward force by ankle pivot = 250 * 0.2/0.05
= 1000 N
=> upward force does the Achilles tendon exert = 1000 - 250
= 750 N
Option D is correct
c) it stretch under this force = (750 * 0.15)/(0.15x1010 * 110 * 10-6)
= 0.68 mm = 0.7 mm
Option B is correct
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