Answer:
c. (H-h/2) above the ground
Explanation:
The mirror must be at least half as tall as the alien, and its base must be located at half of the distance between the alien's eyes and the ground (assuming that the alien doesn't float or levitate).
This question is about the Law of Reflection which states that the angle of reflection = angle of incidence.
I attached an image that can help you understand the concept, although the alien is not included.
Explanation:
It is given that,
The mass of bob, m = 77 kg
Length of the string, L = 10 m
Angle made by the string with the vertical, 
(a) Let T is the force exerted by the string on the pendulum. At equilibrium,



T = 755.63 N
The horizontal component of the force is given by,


The vertical component of the force is given by,


(b) Let a is the radial acceleration of the bob. It can be calculated as :



Hence, this is the required solution.
Answer:
She should explain that the Sun is made up of gaseous layers that surround an iron core.
Explanation:
Given that,
Distance 1, r = 100 m
Intensity, 
If distance 2, r' = 25 m
We need to find the intensity and the intensity level at 25 meters. Intensity and a distance r is given by :
.........(1)
Let I' is the intensity at r'. So,
............(2)
From equation (1) and (2) :



Intensity level is given by :
, 

dB = 32.96 dB
Hence, this is the required solution.
It would not. Imagine four forces equal in magnitude but opposite in direction (e.g. north, east, south, and west). If these forces were to double in magnitude they would still have the same magnitude, meaning the net force is still equal to zero.