On february 15, 2013, a superbolide meteor (brighter than the sun) entered earth’s atmosphere over chelyabinsk, russia, and exploded at an altitude of 23.5 km. eyewitnesses could feel the intense heat from the fireball, and the blast wave from the explosion blew out windows in buildings. the blast wave took approximately 2 minutes 30 seconds to reach ground level. (a) what was the average velocity of the blast wave? b) compare this with the speed of sound, which is 343 m/s at sea level.

156.7m/s, almost half the speed of sound.

Explanation:

23.5 km are 23500m and 2 minutes 30 seconds are 150 seconds.

The formula for average speed is:

The ratio between this and the speed of sound is:

Which means that the average velocity of the blast wave was almost half the speed of sound.

good for her? ? where is the question?

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia