Answer:
The half life of a radioactive substance is 10 days. If you start with 50 grams of the substance, how many grams will be left after 30 days?
First point. Your question is worded fine. As usual, there are folks answering this question saying that “radioactive decay doesn’t reduce mass”. PFUI folks. When an atom decays, it becomes ANOTHER element. THEREFORE, if you started with 50 grams of substance X, after decay you have LESS mass of substance X.
Second point. There is an “easy” way to do this problem, and you got several answers about that. (first half life you drop to 25 gm. Second half life you drop to 12.5 gm. Third half life, and you have 6.25 gm. You can do this one on your fingers.
Now. There is a “hard” way, but it allows you
If you had 16 grams of an element with a half life of 15 minutes would you have 1 gram of mass left after an hour or would its radioactivity only be 1/16th?
Its mass would remain virtually unchanged (diminished very slightly by radiation), but only 1/16 of that mass would still be the original isotope; 15/16 of that mass would now be the daughter isotope (or a granddaughter isotope, or some other descendant, depending on the daughter isotopes' half-lives), which may be either more or less radioactive than the original isotope in question.
The half-life of a certain radioactive element is 35 hours. If there are 904 grams of this element, how much will be left after 70 hours?
If we do your homework for you, you won’t learn anything.
This is a simple problem. Think it through. 35 hours is the half-life so after 35 hours how much is left of the 904g?