The mass of Mg-24 is 24.30506 amu, it contains 12 protons and 12 neutrons.
Theoretical mass of Mg-24:
The theoretical mass of Mg-24 is:
Hydrogen atom mass = 12 × 1.00728 amu = 12.0874 amu
Neutron mass = 12 x 1.008665 amu = 12.104 amu
Theoretical mass = Hydrogen atom mass + Neutron mass = 24.1913 amu
Note that the mass defect is:
Mass defect = Actual mass - Theoretical mass : 24.30506 amu- 24.1913 amu= 0.11376 amu
Calculating the binding energy per nucleon:

So approximately 4.41294 Mev/necleon
Answer : Height, h = 20.4 m
Explanation :
It is given that,
Mass of an object, m = 500 g = 0.5 kg
Gravitational potential energy, PE = 100 J
The Gravitational potential energy is the energy which is possessed due to the height and gravity of an object. It is given as :
PE = m g h
where,
h is the height of the cliff.

h = 20.40 m
So, the height of the cliff is 20.4 m.
A "screen" or even just a set of parallel bars are highly reflective to electromagnetic waves as long as the open spaces are small compared to the wavelengths.
"Grid" dishes work fine ... with less weight and less wind resistance ... for frequencies below about 3 GHz. (Wavelengths of at least 10 cm.)
(I even worked on a microwave system in South America where huge grid dishes were used on a 90-mile link.)
Is 3678.555667775 correct