The Coulomb's force acting between two charges is

where

is the Coulomb's constant, q1 and q2 the two charges, and r the distance between them.
Using

, we can find the distance between the two charges when the force is F=19.2 N:
The net force of a pair of balanced forces is zero
Answer:
2.5 cm
40 D
Explanation:
When the radius of curvature of a lens is divided by 2 we get the focal length of the lens.
Focal length is given by

The focal length of the lens is 2.5 cm
When we divide 1 by the focal length in the unit of meters we get the power of a lens
Power of a lens is given by

The power of the lens is 40 D
Answer:
counterclockwise

Explanation:
= Small drive wheel radius = 2.2 cm
= Angular acceleration of the small drive wheel = 
= Radius of pottery wheel = 28 cm
= Angular acceleration of pottery wheel
As the linear acceleration of the system is conserved we have

The angular acceleration of the pottery wheel is
.
The rubber drive wheel is rotating in clockwise direction so the pottery wheel will rotate counterclockwise.
= Initial angular velocity = 0
= Final angular velocity = 
t = Time taken
From the kinematic equations of linear motion we have

The time it takes the pottery wheel to reach the required speed is 
The net force is the sum of the forces acting on an object ( chair ).
F net = F 1 + F 2
F 1 = 20 N, F 2 = - 12 N
F net = 20 N + ( - 12 N ) = 8 N
The chair will tend to move to the left.