Answer:7.93 m/s
Explanation:
Given
mass of ball 
Mass of hanging ball 
Length of string 
Maximum angle turned 
is the initial velocity of ball 1 and 0 is the initial velocity of ball 2
For Perfectly elastic final velocity of ball 1 and 2 is given by


where
and
are the velocity of 1 and 2 before collision
thus 



By energy conservation on second ball we get
Kinetic energy=Potential Energy




thus 
Answer:

Explanation:
The electric field is defined as the electric force per unit of charge, this is:
.
The electric force can be obtained through Coulomb's law, which states that the electric force between to electrically charged particles is inversely proportional to the square of the distance between them and directly proportional to the product of their charges. The electric force can be expressed as
.
By substitution we get that

Now, letting
be the electric field at point A, letting
be the electric field at point B, and letting R be the distance from the charge to A:
.
The ration of the electric fields is

This means that at half the distance, the electric field is four times stronger.
9,000/12=750
Speed is equal to distance divided by time