For radioactive decay, we can relate current amount, initial amount, decay constant and time using:
N = No x exp(-λt)
Half-life = ln(2)/λ
λ = ln(2) / 5730
N/No = 80% = 0.8
0.8 = exp( -ln(2)/5730 x t)
t = 1844 years
Answer:
B) A piece of metal in water and produces spark and gas
Answer: The amount of heat needed is = 4.3kJ
Explanation:
Amount of heat H = M × C × ΔT
M= mass of benzene = 64.7g
C= specific heat capacity = 1.74J/gK
ΔT = T2-T1
Where T1 is initai temperature = 41.9C
T2 is the final temperature( boiling point of benzene) = 80.1C
H= 64.7×1.74×80.7
H= 4300J
H=4.3kJ
Therefore, the amount of heat needed is 4.3kJ
The answer is C.
This can be concluded by looking at the other answers and eliminating them one-by-one.
Managing (Or conserving) a natural resource means to sustain it and use it as efficiently as possible.
With this in mind, we can look and eliminate certain answers.
A is incorrect because driving a car uses gas, a natural resource. By using as much gas as possible, the resource would be wasted instead of conserved.
B is incorrect because water is a natural resource. Once again, by using this, it's wasted where it could be conserved.
C is correct because planting trees would conserve the resource; by consistently planting trees where they're cut, the chances of running out of wood decrease.
D is incorrect because both the water and the creatures that live inside it are natural resources. By dumping toxic waste, these resources are wasted where it could be conserved.
Hope this helped you! :)
Universe, Stars, Planets, Asteroids
