Answer :
Final answer:
A 10 kg rock of uranium-235 would weigh 5 kg after 700 million years, as half of the uranium-235 would have decayed by then.
Explanation:
Uranium-235 has a half-life of 700 million years, which means that after 700 million years, half of the original amount of uranium-235 will have decayed into other elements. To determine how much a 10 kg rock of uranium-235 would weigh after 700 million years, we can use the concept of exponential decay.
Since the half-life is 700 million years, after 700 million years, half of the uranium-235 in the rock will have decayed. This means that after 700 million years, the rock would weigh 5 kg.
Similarly, after another 700 million years, half of the remaining 5 kg would decay, leaving behind 2.5 kg. This process continues, with each half-life reducing the weight by half. So, after several half-lives, the weight of the rock will approach zero, but it will never fully reach zero. The decay process continues indefinitely.
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