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27 September, 23:20

There is a 30 g sample of Be-11. It has a half-life of about 14 seconds. How much will be left after 28 seconds? A. 3.75 gB. 7.5 gC. 15 gD. 30 g

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  1. 28 September, 00:18
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    After 28 sec 7.5 grams of Be will be left

    Explanation:

    Given dа ta:

    Total amount of Be = 30 g

    Half life of Be = 14 sec

    Mass left after 28 sec = ?

    Solution:

    First of all we will calculate the number of half lives in 28 sec.

    Number of half lives = T elapsed / half life

    Number of half lives = 28 sec / 14 sec

    Number of half lives = 2

    AT time zero = 30 g

    At first half life = 30 g/2 = 15 g

    At second half life = 15 g / 2 = 7.5 g

    So after 28 sec 7.5 grams of Be will be left.
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