An original sample of K-40 has a mass of 25.00 grams.
After 3.9 m 109 years, 3.125 grams of the original sample remains unchanged.
What is the half-life of K-40?
First step is to determine the remaining decimal amount.
3.125 grams /25.00 grams = 0.125
Second step is to determine the number of half lives.
(1/2)^n = 0.125
N log (1/2) = log 0.125
N = 3 years
Answer:
Because Scientists Uses hypothesis and try tests and try proving their points while regular normal people use it to just state a statement
The energy needed to raise the temperature of water from 22.0ºC to 90.0ºC is c. 28.4 kJ.
<h3>What is specific heat?</h3>
The amount of energy needed to raise the temperature of one gram of a substance by one degree Celsius.
By the formula 
Q is the heat
m is the mass
c is the specific heat
Now, c = 4.184 J/g.K
The change in temperature is 22.0 ºC to 90.0 ºC
Putting the value in the equation

Thus, the energy needed to raise the temperature of water from 22.0ºC to 90.0ºC is 28.4 kJ
Learn more about specific heat
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