A proton is released from rest , 10 cm from a charged sheet carrying charge density of $\;-2.21\times10^{-9}\;c/m^2\;.$ It will strike the sheet after time $\;(approximately)$

Question

$(a)\;4\;\mu s\qquad(b)\;2\;\mu s\qquad(c)\;2 \sqrt{2}\;\mu s\qquad(d)\;4 \sqrt{2}\;\mu s$

Comments

But the electric field of a charged sheet is sigma by 2 epsilon nought