How many electron would have to ejected from a body to descrease its mass by 0.03 milligrams. The mass of one electron is 9.1*10 the minus 31kg?

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Answer 1 · 2018-07-08T15:49:38

Approximately $3.3 \cdot 10^{21}$ $3.3*10^21$ electrons.

The mass of an electron is:

$m_(e^-)=9.1*10^-31 \ "kg"$

Note that $1 \ "kg"-=1*10^6 \ "mg"$ . So the mass of an electron in milligrams will be:

$m_(e^-)=9.1*10^-31color(red)cancelcolor(black)"kg"*(10^6 \ "mg")/(color(red)cancelcolor(black)"kg")=9.1*10^-25 \ "mg"$

In order to reduce the mass of a body by $0.03 \ "mg"=3*10^-2 \ "mg"$ , then a total of:

$(3*10^-2color(red)cancelcolor(black)"mg")/(9.1*10^-25color(red)cancelcolor(black)"mg""/"e^-)~~3.3*10^21 \ e^-$

must be released.