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 with a typical 1.1×10−4m2 area.
A. By how much will the runner's Achilles tendon stretch if theforce on it is 8.0 times his weight?
B. What fraction of the tendon's length does this correspond?

Explanation:

Given:

Mass, M = 70 kg

Area, A = 1.1 × 10^-4 m^2

Achilles tendon length, l = 15 cm

= 0.15 m

Young modulus for tendon, E = 0.15 × 10^10 N/m^2

Young modulus, E = tensile stress/tensile strain

But,

Stress = force/area

Strain = extension/length

A.

Force = 8 × N

N = m × g

= 70 × 9.8 × 8

= 5488 N

Extension = (force × length)/(area × yound modulus)

= (5488 × 0.15)/(1.1 × 10^-4 × 0.15 × 10^10)

= 4.989 mm

= 0.005 m

B.

Fraction of length, x = extension/original length

= 0.005/0.15

= 0.033

= 3.3 %

so here is the information for current research:

-nrel's geothermal analysts, scientists, and engineers perform a full range of research from developing advanced methods of locating and accessing geothermal resources to exploring innovative technologies to extract and produce clean energy from the heat of the earth

and here is the information for the technology of geothermal energy:

-it's clean and sustainable

-resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the earth's surface, and down even deeper to the extremely high temperatures of molten rock called magma

-almost everywhere, the shallow ground or upper 10 feet of the earth's surface maintains a nearly constant temperature between 50° and 60°f (10° and 16°c)

-geothermal heat pumps can tap into this resource to heat and cool buildings

-a geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger-a system of pipes buried in the shallow ground near the building

-in the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system

-in the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger

-the heat removed from the indoor air during the summer can also be used to provide a free source of hot water