Answer:
11.3 g
Explanation:
given,
density of the lead = 11.3 g/cm³
volume = 1 cm³
mass of the lead = ?
we know,

mass = volume x density
mass = 1 x 11.3
mass = 11.3 g
hence, the mass of the lead is equal to 11.3 g
A radar receiver indicates that a pulse return as an echo in 20 μs after it was sent. The reflecting object would be 3000 m away .
Phenomenon of hearing back our own sound is called an echo. It is due to successive reflection of sound waves from the surfaces or obstacles of large size. To hear an echo, there must be a time gap of 0.1 second in original sound and the reflected sound.
Given
time = 20 μs = 20 *
s
let distance to the reflecting surface be = x
total distance travelled by pulse will be = 2x
speed = 3.0 ×
m/s
distance = speed * time
2x = 3.0 ×
* 20 *
x = 3000 m
The reflecting object would be 3000 m away
To learn more about echo here
brainly.com/question/14861578?referrer=searchResults
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The force ffrom the ground that holds the rock up and prevents her from falling through the gound, unless the ground breaks.
A) seismic waves
b) sound waves
sound waves are traveling vibrations of particles in media (air, water, metal, etc) so they can’t travel through empty space (vacuums) because there are no atoms or molecules to vibrate.
seismic waves are mechanical waves and require a medium for propagation, hence, they cannot travel through a vacuum.
hope this helps :)