Gastrocnemius muscle tension

[valeriex0x]

Homework Statement

The gastrocnemius muscle, in the back of the leg, has two portions, known as the medial and lateral heads. Assume that they attach to the Achilles tendon as shown in the figure. The cross-sectional area of each of these two muscles is typically 30 cm^2 for many adults.
What is the maximum tension they can produce in the Achilles tendon? (Muscles are attached to bones by means of tendons. The maximum force that a muscle can exert is directly proportional to its cross-sectional area at the widest point. We can express this relationship mathematically as Fmax=sigma A , where (sigma) is a proportionality constant. Surprisingly, sigma is about the same for the muscles of all animals and has the numerical value of 3.10 x 10^5 in SI units.)

Tmax= ? N

Homework Equations

free body diagram

The Attempt at a Solution

I got it wrong. But i did:
fmax= 3.0 x 10^5 * 30cm= 9.3X10^6

I'm not sure how to approach the problem...

 

[gneill]

Does sigma (σ) have any units attached to it? In other words, does it express force per square centimeter or force per square meter?

Also, why did you multiply by three : fmax= 3.0 x 10^5 * 30cm= 9.3X10^6
Also, the units of area should be cm², not just cm.