Answer:1.71 m/s
Explanation:
Given
mass of Susan 
Inclination 
Tension 
coefficient of Friction 
Resolving Forces Along x axis

where

since there is no movement in Y direction therefore

and 
Thus 


Work done by applied Force is equal to change to kinetic Energy




Divide
(the distance covered in some period of time)
by
(the time taken to cover the distance).
The quotient is the average speed during that period of time.
relation between potential difference and electric field is given as

so here we know that
d = 3 cm



So now when plates are separated to 4 cm distance carefully
the potential difference between them will change but the electric field between them will remain constant
So at distance of 4 cm also the electric field will be E = 1000 N/C