Answer:
EXAMPLE:when you jump, your legs apply a force to the ground, and the ground applies and equal and opposite reaction force that propels you into the air.
The question is missing, however, I guess the problem is asking for the value of the force acting between the two balls.
The Coulomb force between the two balls is:

where

is the Coulomb's constant,

is the intensity of the two charges, and

is the distance between them.
Substituting these numbers into the equation, we get

The force is repulsive, because the charges have same sign and so they repel each other.
Answer:


-0.020475 V
Explanation:
= Vacuum permeability = 
= Number of turns of coil = 25
= Number of turns of coil 2 = 300
= Rate of current increased = 
d = Diameter = 2 cm
r = Radius = 
A = Area = 
Magnetic field in the solenoid is given by

Magnetic flux is given by

The average magnetic flux through each turn of the inner solenoid is
Mutual inductance is given by

The mutual inductance of the two solenoids is 
Induced emf is given by

The emf induced in the outer solenoid by the changing current in the inner solenoid is -0.020475 V
Answer:
Yes
Explanation:
The velocity measured by Jennifer and Johnny is

The actual velocity is

We can calculate the % error of the students measurement as follows:

Which is lower than the 2.5% maximum error required, so the two students will pass the test.