1) The half-life is the time required for a substance to reduce to half its initial value. In formulas:
(1)
where
m(t) is the amount of substance left at time t
m0 is the initial mass
is the half-life
In this problem, the half-life of the substance is 20 years:
therefore, the fraction of sample left after t=40 years will be
So, only 1/4 of the original sample will be left, which corresponds to 25%.
2) We can use again formula (1), by re-arranging it:
If we use m(t)=10 g (mass of uranium left at time t), and
(the time is equal to 4 half lifes), we get
So, the initial sample of uranium was 160 g.
Answer:
the potentail of kinetic and potential energy
Explanation:
first explain the concept of kinetic energy (what it is and what its used for) and give examples (cars, a basketball thrown across a hall, and airplane), and do the same with potential energy (the energy an object stores, example: a streched rubber band)
the answer is a: galaxies. galaxy clusters are groups of galaxies that like to hang out together out there in space. the milky way's own galaxy cluster is called the local group.
The paper clip did because it is a conductor. A pencil is made with wood and that is an insulator.
The partial pressure of nitrogen is about 584 mmHg.