Answer:
Explanation:
Given:
Initial mass of isotope (m₀) = 20 g
Half life of the isotope 
= (ln 4) years
The general form for the radioactive decay of a radioactive isotope is given as:
Where,
So, the equation is: 
At half-life, the mass is reduced to half of the initial value.
So, at 
. Plug in these values and solve for 'k'. This gives,
Hence, the equation for the mass remaining is given as:
The forces are in equilibrium.
Answer:
Concrete absorbs visible light and re-radiates it as infrared energy.
Explanation:
As we know that concrete will not reflect 100% light incident on it but it will absorb few energy and remaining energy is reflected back.
So here when visible light incident on the concrete then few of its energy is absorbed by is and then the remaining energy is reflected back.
Since the reflected energy must be less than the energy which incident on the concrete so here we will say that the reflected waves must be of less frequency range
so here most appropriate energy range of reflected wave is infrared waves
so here correct answer will be
Concrete absorbs visible light and re-radiates it as infrared energy.
I believe the answer would be 446.9 J.
Yes a igneous rock can be changed into another igneous rock. the reason behind it is when rocks melt they become magma or lava. when lava flows on the surface of the earth it crystallizes quickly and makes small crystals. but when they cool slower they make larger crystals. yes igneous rocks can change but only through extreme temperatures.
