Aswimmer heading directly across a river 200 m wide reaches the opposite bank in 6 min 40 s, during which time she is swept downstream 480m. how fast can she swim in still water

Short method:

Assuming the direction that she is swimming is directly across the river (y-direction), and she is swept downstream (x-direction) by the current in the river. We can directly calculate her y-velocity:

y = v*t

v = y/t = 200/(6*60 + 40) = 0.5 m/s

Long method:

The river’s speed does not contribute to her progress across the river. It only provides an x-direction component. If we want to calculate her component of velocity over the resultant path, we would calculate the resultant distance and velocity.

v_x = 480m/400s = 1.2 m/s

v_x is the speed of the river current

The distance covered is calculated using hypotenuse formula:

d = sqrt(200^2 + 480^2) = 520 m

The resultant velocity is:

v = d/t = 520/400 = 1.3 m/s

However this is still the resultant speed of the swimmer and the river current together. Therefore using the hypotenuse formula again to find for v_x:

v^2 = v_x)^2 + (v_y)^2

v^2 - (v_x)^2 = (v_x)^2

v_y = sqrt [ v^2 - (v_x)^2 ] = sqrt( 1.3^2 - 1.2^2) = 0.5 m/s

This is the swimmers velocity without the current.

0.5 m/s

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:

answer;

d. are made mostly of liquid

explanation;

-the general   composition and structure planets includes; they have a thick gas and liquid layer covering a small,solid core. mostly the gases are hydrogen and helium atmosphere and layers of liquid hydrogen. for instance neptune and uranus are examples of the outer planets, they have a core covered by ice and ammonia.

-neptune's atmosphere is hydrogen and helium with a bit of methane so there is no oxygen to breath and the interior is made up of frozen water and ammonia with a rock and iron core. thus, there is no liquid water or solid surface to survive.