# 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?

Jul 8, 2018

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

#### Explanation:

The mass of an electron is:

${m}_{{e}^{-}} = 9.1 \cdot {10}^{-} 31 \setminus \text{kg}$

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

${m}_{{e}^{-}} = 9.1 \cdot {10}^{-} 31 \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{kg"*(10^6 \ "mg")/(color(red)cancelcolor(black)"kg")=9.1*10^-25 \ "mg}}}}$

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

$\left(3 \cdot {10}^{-} 2 \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{mg")/(9.1*10^-25color(red)cancelcolor(black)"mg""/}}}} {e}^{-}\right) \approx 3.3 \cdot {10}^{21} \setminus {e}^{-}$

must be released.