N° 6 : Bats produce sound waves of 50000 to 200000 vibrations per second These waves hit the obstacles and an echo that is extremely accurate returns. Bats capture the echo with their very
sensitive and developed ears: as a result they know the position of the obstacle precisely.
1) a) Pick up the domain of frequencies emitted by the bat in Hz.
b) Are these waves audible by the human ear ? Why?
from the text the sentence which mentions a physical phenomenon.
c) Pick
up
2) A bat sends a wave of 100 kHz towards an
obstacle situated at a distance d = 2 m and
receives the echo after a time «t».
Given that the speed of sound waves in air
)
Obstacle
330 m/s.
a) Calculate the period and the wavelength of
the waves emitted in air.
b) Find the distance « D » covered by the wave after leaving the bat and till its return to the bat.
c) Deduce, in ms, the duration (emission - reception) denoted by «t».​

In physics the desire of an object to keep doing what it is doing is termed?

If steel is more dense that lake water, why can a boat float

Clothing made of several thin layers of fabric with trapped air in between, often called ski clothing, is commonly used in cold climates because it is light, fashionable, and a very effective thermal insulator. so it is no surprise that such clothing has largely replaced thickand heavy old-fashioned coats. (a) consider a jacket made of five layers of 0.1-mm-thick synthetic fabric (k = 0.13 w/m·°c) with 1.5-mm-thick air space (k = 0.026 w/m·°c) between the layers. assuming the inner surface temperature of the jacket to be 28°c and the surface area to be 1.25 m2, determine the rate of heat loss through the jacket when the temperature of the outdoors is 0°c and the heat transfer coefficient at the outer surface is 25 w/m2·°c. (b) what would your response be if the jacket is made of a single layer of 0.5-mm-thick synthetic fabric? what should be the thickness of a wool fabric (k = 0.035 w/m·°c) if the person is to achieve the same level of thermal comfort wearing a thick wool coat instead of a five-layer ski jacket?