Physics
posted by Schrei .
The Achilles tendon, which connects the calf muscles to the heel, is the thickest and strongest tendon in the body. In extreme activities, such as sprinting, it can be subjected to forces as high as 13.0 times a person's weight. According to one set of experiments, the average area of the Achilles tendon is 78.1 mm^2, its average length is 25.0 cm, and its average Young's modulus is 1474 MPa.
How much tensile stress is required to stretch this muscle by 5.00 % of its length?
.05=F(parallel)/A /Y
F(par)=
A=
Y=
If we model the tendon as a spring, what is its force constant?
If a 75.0 kg sprinter exerts a force of 13.0 times his weight on his Achilles tendon, by how much will it stretch?
F=kx
F=13*75*9.8=9555
k=value for above part
x=solve for

You have the formulas, and the numbers to input. Why don't you just do the calculations?
For the second question, the force constant would be F(par)/(delta L)
= A Y/L