I would say B. Because actual mass would ricochet off the sidewalk.
Answer: a) 8.2 * 10^-8 N or 82 nN and b) is repulsive
Explanation: To solve this problem we have to use the Coulomb force for two point charged, it is given by:

Replacing the dat we obtain F=82 nN.
The force is repulsive because the points charged have the same sign.
Answer:
the object is decelerating
Answer:
19.6N
Explanation:
Given parameters:
Mass of rock = 2kg
Speed = 30m/s
Unknown:
Net force on the rock = ?
Solution:
The net force acting on this rock is a function of the acceleration due to gravity acting upon it.
Net force = weight = mass x acceleration due to gravity
Net force = 2 x 9.8 = 19.6N downward