The achilles tendon connects the muscles in your calf to the back of your foot. when you are sprinting, your achilles tendon alternately stretches, as you bring your weight down onto your forward foot, and contracts to push you off the ground. a 70 kg runner has an achilles tendon that is 15 cm long and has a cross-section area of 110mm2, typical values for a person of this size. a. by how much will the runner's achilles tendon stretch of the maximum force on it is 8.0 times his weight, a typical value while running? b. what fraction of the tendon's length does this correspond to?

(a)

(b)0.033

Explanation:

(a)

Force F=mg where m is mass and g is acceleration due to gravity whose value is taken as

However, for this case, the maximum force is 8 times the weight of runner hence F=8mg

Assume Young's modulus for tendon is

Young's modulus is given by

and and substituting F with 8mg we obtain

Where E is young's modulus, l is stretched length and \triangle l is change in length

Substituting m as 70 kg, g as , l as 15cm=0.15 m, E as and A as

(b)

Strain, and the fraction of tendon’s length is the ratio of change in length to the stretched length

The fraction of tendon, f is given by

. Substituting with 0.005m and l with 0.15m we obtain

Therefore, fraction of the tendon’s length is 0.033

power out to power in less than 100%

need to see circuit to get time constant