Repeal above exercise for a proton which is made of two up and one down quark.

Explanation

For proton two up and one down quark

`q_(d)= -(1)/(3)e`
`q_(u) = +(2)/(3) e`
`r=10^(-15)` m
`:.` Potential energy of system
`U =k[(q_(u)q_(u))/(r)+(q_(u)q_(d))/(r)+(q_(u)d_(d))/(r)]`

`=k[((2)/(3)exx(2)/(3)e)/(r)+((2)/(3)exx(-(1)/(3)e))/(r)+((2)/(3)exx(-(1)/(3)e))/(r)]`
`=(k)/(r)[(4)/(9)e^(2)-(2)/(9)e^(2)-(2)/(9)e^(2)]`
`=(ke^(2))/(9r)[4-2-2]`
`=(ke^(2))/(9r)[0]`
=0
`:.` Ratio of potential energy of proton to iti mass is zero