The force exerted by Earth plays the role of centripetal force.
Answer:
Magnitude of electric field at mid way is 
Solution:
As per the question:
Q = 
Q' = 
Separation distance, d = 9.0 cm = 0.09 m
The distance between charges at mid-way, O is 
Now, the electric at point O due to charge Q is:





Here, negative sign is indicative of the direction of electric field which is towards the point O
Now, the electric at point O due to charge Q' is:



Refer to Fig 1.
Since, both the fields are in the same direction:

v = u + a t => t = v/a = 65/3 sec
s = u t + 1/2 a t² = 1/2 * 3 * 65²/3² = 704.6 meters
hop it helps
D I took the quiz and I'm pretty sure you will get it correct