Question

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?

Answer 1

Approximately `3.3*10^21` electrons.

Explanation:

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.