Tv broadcast antennas are the tallest artificial structures on earth. in 1987, a 79.0 kg physicist placed himself and 400 kg of equipment at the top of one 610 m high antenna to perform gravity experiments. by how much (in mm) was the antenna compressed, if we consider it to be equivalent to a steel cylinder 0.125 m in radius? (assume a young's modulus of 20 ⨯ 1010 pa.)

m

Explanation:

= mass of physicist and his equipment together = 79 + 400 = 479 kg

Force applied by weight of physicist and his equipment together on the antenna is given as

N

= original length of the antenna = 610 m

= compression in the length of the antenna

= radius of the cylinder = 0.125 m

Area of cross-section of the cylinder is given as

m²

= Young's modulus of steel = 20 x 10¹⁰ Pa

Young's modulus is given as

Inserting the above values

m

nec chapter 5 contains

c. information on special occupancy areas

nec chapter 6 covers

a. special equipment

which of the following rules contain the words shall or shall not and must be adhered to?

b. mandatory rules

which of the following rules identify actions that are allowed but not required and typically cover options or alternative methods?

c. optional rules

which of the following serves as the introduction to the nec and provides an overview of the book?

a. nec article 90

organizations that test products for safety are

c. nrtls

the nec is published by the

a national fire protection association

the nec is divided into

b. 9 chapters

the nec provides informative annexes for

c. informational materials and examples

two terms from nec article 100 that trainees should become familiar with are

b. labeled and listed

explanation: