A boy on a bicycle approaches a brick wall as he sounds his horn at a frequency 400 Hz. The sound he hears reflected back from the wall is at a frequency 408 Hz. At what speed is the boy riding his bicycle toward the wall

6.8 m/s

Explanation:

To solve this, we would use the Doppler's Effect. Doppler's effect is represented by the formula

f = [(g + vr)/(g + vs)].fo, where

f = observed frequency, 408 Hz

g = speed of sound in air, 340 m/s

vr = velocity of the receiver

vs = velocity of the source, 0 m/s

fo = source frequency, 400 Hz

Now, applying the values to the equation, we have

408 = [(340 + vr)/(340 + 0) * 400

408/400 = (340 + vr)/340

1.02 * 340 = 340 + vr

346.8 = 340 + vr

vr = 346.8 - 340

vr = 6.8 m/s

Therefore the speed at which the boy is riding his bicycle towards the wall is 6.8 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:

pecialized keyboards