Because it demonstrates the relationship between a body and the forces acting upon it, and its motion in response to those forces. [Hope that helps]
Answer:
D. 4000 km
Explanation:
f = Frequency of wave that is being transmitted = 76 Hz
= Wavelength of wave that is being transmitted
v = The velocity of electromagnetic waves through air = 
Velocity of a wave is given by

Hence, the approximate wavelength of the waves is 4000 km
The area is the length times the height so A= bh ...?
The answer is a lense since mirrors reflect light