A radioactive element with a half-life of 1,000 years, and starting mass of 20 grams, will need 2,000 years to decrease to 5 grams.
Explanation:
The radioactive elements all have a specific half-life. Each element's half-life is well known, and they are used by scientists of numerous fields as they are excellent for determining the age of a particular item, be it or organic or non-organic nature. In this case, we have a radioactive element with a half-life of 1,000 years, and starting mass of 20 grams.
The half-life basically means that half of the mass of an element is lost during a particular period of time. For the element in question we need to find out how much time will be needed for it to decrease to 5 grams. In order to get to the result, we just need to add 1,000 years on every decrease of half of the mass:
20/2 = 10
10/2 = 5
So in 1,000 years, the element in question will decrease to 10 grams, and in further 1,000 years (2,000 cumulatively) it will decrease to 5 grams.
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În timpul unei eclipse de Lună, Pământul trece între Lună și Soare, determinând Pământul să-și arunce umbra asupra Lunii.
Veți observa că umbra pe care o produce este rotundă. Chiar dacă Pământul ar fi plat, dar în formă de disc, nu ar arunca nici acest gen de umbră. „Singura formă care poate produce o umbră curbată, indiferent din ce direcție este plasată lumina, este o sferă”, explică Thaller.
Weather is determined by the values of meteorological factors: temperature, air umididatea, wind direction and speed, atmospheric pressure, air turbulence, the amount and type of precipitation. These factors are measured by specific instruments - thermometers, barometers, hydrometers, weathervane to The measured values over long periods of time (years or decades) statistically give us information about the climate of a region.
The answer is obviously 64.